HreiE 


1 


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LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

GIFT    OF 

...GEN....CJiAS,....Jl.....G.J^EJENLEAF..... 

BIOLOGY 
LIBRARY 


ABSORPTION    SPECTRA 


1.  Spectrum  of  Ar gaud-lamp  with  Fraunhofefs  lines  in  position. 

2.  Blood;  ie.  a  strong  solution  of  Oxyhasmoglobm  fciemc 
3. Blood  more  dilute. 

4.  Reduced  Hsemoglobin.  5. Carbon  Monoxide  compound. 

6.  Acid  Hsematin.  .        7.  Alkaline  Hasmatin . 

8.  Sulphuretted  Hydro  gen  compound.  9.  Ox-Me  acidulated  with  Acetic  acid 
and  colouring  natter  dissolved  in  Chloroform.. 

((mn'/t  fror/t  observations fyrMr.WZepraik>-F'.C.S. 


1885, 


KTEKES1  HlOTD-BOOK  OF  PHYSIOLOGY 


HAKD-BOOK 


OP 


PHYSIOLOGY 


BY 

AV.   MOKBANT   BAKEE,   F'.E.O.S. 

SURGEON  TO  ST.   BARTHOLOMEW'S  HOSPITAL  AND  CONSULTING  SURGEON  TO  THE  EVELINA  HOSPITAL 

FOR    SICK    CHILDREN;     LECTURER    ON    PHYSIOLOGY    AT   ST.    BARTHOLOMEW'S    HOSPITAL, 

AND   LATE  MEMBER  OF  THE  BOARD  OF  EXAMINERS  OF  THE  ROYAL  COLLEGE 

OF  SURGEONS  OF  ENGLAND. 

AND 

VINCENT  DOEMEE  HAEEIS.  M.D.,  LOND. 

DEMONSTRATOR  OF  PHYSIOLOGY  AT  ST.   BARTHOLOMEW'S  HOSPITAL. 


ELEVENTH    EDITION 


WITH    NEARLY  BOO   ILLUSTRATIONS 


VOLUME  I 


(   UNIVERSITY  | 


NEW  YORK 

WILLIAM    WOOD    &    COMPANY 
56  &  58  LAFAYETTE  PLACE 

1885 


BIOLOGY 

LIBRARY 

G 


THE  PUBLISHERS' 

BOOK  COMPOSITION  AND  ELECTROTYPING  Co., 

39  AND  41  PARK  PLACE, 

NEW  YORK. 


PREFACE  TO  THE  ELEVENTH  EDITION. 


IN  the  preparation  of  the  present  edition  of  Kirkes'  Physiology, 
we  have  endeavored  to  maintain  its  character  as  a  guide  for  stu- 
dents, especially  at  an  early  period  of  their  career;  and,  while 
incorporating  new  facts  and  observations  which  are  fairly  estab- 
lished, we  have  as  far  as  possible  omitted  the  controvertible  matters 
which  should  only  find  a  place  in  a  complete  treatise  or  in  a  work  of 
reference. 

A  large  number  of  new  illustrations  have  been  added,  for  many 
of  which  we  are  indebted  to  the  courtesy  of  Dr.  Klein,  Professor 
Michael  Foster,  Professor  Schaefer,  Dr.  Mahomed,  Mr.  Gant,  and 
Messrs.  McMillan,  who  have  been  so  good  as  to  allow  various  figures 
to  be  copied.  Our  thanks  are  also  due  to  Mr.  Wm.  Lapraik,  F.C.S., 
who  has  kindly  prepared  a  table  of  the  absorption  spectra  of  the 
blood  and  bile,  based  upon  his  own  observations;  as  well  as  to  Mr. 
S.  K.  Alcock  for  several  careful  drawings  of  microscopical  prepara- 
tions, and  for  reading  several  sheets  in  their  passage  through  the 
press. 

Mr.  Danielsson,  of  the  firm  of  Lebon  &  Co.,  has  executed  all  the 
new  figures  to  our  entire  satisfaction ;  and  for  the  skill  and  labor  he 
has  expended  upon  them  we  are  much  indebted  to  him. 

We  are  desirous  also  of  acknowledging  the  help  we  have  derived 
from  the  following  works :  Klein's  Histology ;  M.  Foster's  Text-Book 
of  Physiology;  Pavy's  Food  and  Dietetics;  Quain's  Anatomy,  Yol. 
II.,  Ed.  ix. ;  Wickham  Legg's  Bile,  Jaundice,  and  Bilious  Diseases ; 

218839 


IV  PREFACE. 


Watney's  Minute  Anatomy  of  the  Thymus ;  Rosenthal's  Muscles  and 
Nerves  ;  Cadiat's  Traite"  D'Anatomie  Ge'ne'rale  ;  Ranvier's  Traite" 
Technique  D'Histologie  ;  Landois'  Lehrbuch  der  Physiologie  des 
Menschen,  and  the  Journal  of  Physiology. 


WIMPOLE  STREET, 

August,  1884. 


W.  MORRANT  BAKER. 
V.  D.  HARRIS. 


TO   VOLUME   I. 


CHAPTER  I. 

PAGE 

THE  GENERAL  AND  DISTINCTIVE  CHARACTERS  OF  LIVING  BEINGS  1 


CHAPTER  II. 

STRUCTURAL  BASIS  OF  THE  HUMAN  BODY 5 

Cells 5 

Protoplasm 6 

Nucleus          .............  10 

Intercellular  Substance          .        ...        .        .        .        .        .        .        .17 

Fibres 17 

Tubules 17 

CHAPTER  III. 

STRUCTURE  OF  THE  ELEMENTARY  TISSUES 19 

Epithelium 19 

Connective  Tissues        ...........  28 

Areolar  Tissue        ...........  31 

White  Fibrous  Tissue 31 

Yellow  Elastic  Tissue 32 

Gelatinous 33 

Retiform  or  Adenoid 34 

Xeuroglia 34 

Adipose  .                 35 

Cartilage 38 

Bone ...  42 

Teeth 05 

CHAPTER  IV. 

THE  BLOOD 63 

Quantity  of  Blood 63 

Coagulation  of  the  Blood     ..........  65 

Conditions  affecting  Coagulation  .........  71 

The  Blood  Corpuscles 74 


Vi  CONTENTS. 

THE  BLOOD — Continued. 

PAGE 

Physical  and  Chemical  Characters  of  Red  Blood-Cells         .        .  -      .        .  75 

The  White  Corpuscles,  or  Blood-Leucocytes 79 

Chemical  Composition  of  the  Blood              , 83 

The  Serum 85 

Variations  in  Healthy  Blood  under  Different  Circumstances       ...  86 

Variations  in  the  Composition  of  the  Blood  in  Different  Parts  of  the  Body  87 

Gases  contained  in  the  Blood 88 

Blood-Crystals 91 

Development  of  the  Blood             96 

Uses  of  the  Blood 99 

Uses  of  the  various  Constituents  of  the  Blood 99 


CHAPTER  V. 

ClKCTJLATION  OF  THE  BLOOD 101 

The  Systemic,  Pulmonary,  and  Portal  Circulations 102 

The  Forces  concerned  in  the  Circulation  of  the  Blood         ....  103 

THE  HEART 103 

Structure  of  the  Valves  of  the  Heart Ill 

The  Action  of  the  Heart        .        .        .        . Ill 

Function  of  the  Valves  of  the  Heart 112 

Sounds  of  the  Heart      .        .        .        . 117 

Impulse  of  the  Heart .        .        .        .119 

The  Cardiograph 119 

Frequency  and  Force  of  the  Heart's  Action        ...._..  122 

Influence  of  the  Nervous  System  on  the  Action  of  the  Heart      .        .        .  124 

Effects  of  the  Heart's  Action .        .  127 

THE  ARTERIES.  CAPILLARIES,  AND  VEINS 128 

Structure  of  the  Arteries 129 

Structure  of  Capillaries        . 133 

Structure  of  Veins         .        .        ....        .        .        .        .        .  136 

Function  of  the  Arteries        .        ....        .        .        .        .        .  138 

The  Pulse 142 

Sphygmograph      .        . 143 

Pressure  of  the  Blood  in  the  Arteries,  or  Arterial  Tension  .        .        .148 

The  Kymograph     .        .        .        .        .....        .        .        .  150 

Influence  of  the  Nervous  System  on  the  Arteries         .        ,        .        .        .  152 

Circulation  in  the  Capillaries         .         .         .         .                 .         .         .         .  158 

Diapedesis  of  Blood-Corpuscles    .        ...        .        .        .        .        .  159 

CIRCULATION  IN  THE  VEINS       .        , 161 

Blood-pressure  in  the  Veins ,        .        .        .162 

Velocity  of  the  Circulation   ...         .         .  .         .         .         .163 

Velocity  of  the  Blood  in  the  Arteries    . 164 

Capillaries 165 

Veins       .         . 165 

Velocity  of  the  Circulation  as  a  whole          .......  166 


CONTENTS.  Vll 

PAGE 

PECULIARITIES  OP  THE  CIRCULATION  IN  DIFFERENT  PARTS  ....  167 

Circulation  in  the  Brain 167 

Circulation  in  the  Erectile  Structures .  168 

Agents  concerned  in  the  Circulation 170 

•  Discovery  of  the  Circulation 170 

Proofs  of  the  Circulation  of  the  Blood 171 

CHAPTER  VI. 

RESPIRATION        .        .        . . .  172 

Position  and  Structure  of  the  Lungs 173 

Structure  of  the  Trachea  and  Bronchial  Tubes 176 

Structure  of  Lobules  of  the  Lungs .        .  178 

Mechanism  of  Respiration    ..........  183 

Respiratory  Movements         ..........  183 

Respiratory  Rhythm 188 

Respiratory  Sounds       .        .        .        .        .        .        .        .        .        .        .  188 

Respiratory  Movements  of  Glottis 188 

Quantity  of  Air  Respired 189 

Vital  or  Respiratory  Capacity 190 

Force  exerted  in  Respiration 191 

Circulation  of  Blood  in  the  Respiratory  Organs 191 

Changes  of  the  Air  in  Respiration 192 

Changes  produced  in  the  Blood  by  Respiration 198 

Mechanism  of  various  Respiratory  Actions 198 

Influence  of  the  Nervous  System  in  Respiration 201 

Effects  of  Vitiated  Air— Ventilation 204 

Effect  of  Respiration  on  the  Circulation       .        .        .        .        .        .        .  205 

Apnoea — Dyspnoea — Asphyxia 209 

CHAPTER  VII. 

FOODS 212 

Classification  of  Foods 213 

Foods  containing  chiefly  Nitrogenous  Bodies 214 

Carbohydrate  Bodies 216 

Fatty  Bodies 217 

Substances  supplying  the  Salts 217 

Liquid  Foods 217 

Effects  of  Cooking 217 

Effects  of  an  Insufficient  Diet 218 

Starvation 219 

Effects  of  Improper  Food 221 

Effects  of  too  much  Food 222 

Evict  Scale 223 

CHAPTER  VIII. 

DIGESTION 224 

PASSAGE  OF  FOOD  THROUGH  THE  ALIMENTARY  CANAL 224 

Mastication 224 

Insalivation   ....  22G 


Vlll  CONTENTS. 

PASSAGE  OF  FOOD,  ETC. — Continued. 

PAGE 

The  Salivary  Glands  and  the  Saliva .  226 

Structure  of  the  Salivary  Glands '  .  226 

The  Saliva 229 

Influence  of  the  Nervous  System  on  the  Secretion  of  Saliva        .       • .        .  231 

The  Pharnyx 236 

The  Tonsils 236 

The  (Esophagus  or  Gullet        ..        .         . 236 

Swallowing  or  Deglutition    .        .        .        .  -,      .        .        .        .        .        .  238 

DIGESTION  OP  FOOD  IN  THE  STOMACH     .        .        .        .        .        .        .        .  240 

Structure  of  the  Stomach      . .        .241 

Gastric  Glands       ...        .        . 242 

The  Gastric  Juice .        .        .        .  245 

Functions  of  the  Gastric  Juice 247 

Movements  of  the  Stomach  ..........  249 

Vomiting        .............  251 

Influence  of  the  Nervous  System  on  Gastric  Digestion        ....  252 

Digestion  of  the  Stomach  after  Death 253 

DIGESTION  IN  THE  INTESTINES  ..........  254 

Structure  of  the  Small  Intestine .        .        .254 

Valvulse  Conniventes 255 

Glands  of  the  Small  Intestine 257 

TheVilli 259 

Structure  of  the  Large  Intestine 263 

The  Pancreas  and  its  Secretion 264 

Structure  of  the  Liver ;         ...  268 

Functions  of  the  Liver 273 

The  Bile 273 

The  Liver  as  a  Blood-elaborating  Organ 280 

Glycogenic  Function  of  the  Liver        ........  280 

Summary  of  the  Changes  which  take  place  in  the  Food  during  its  Passage 

through  the  Small  Intestine 284 

Succus  Entericus 283 

Summary  of  the  Process  of  Digestion  in  the  Large  Intestine       .        .        .  286 

Defsecation 288 

Gases  contained  in  the  Stomach  and  Intestines .  288 

Movements  of  the  Intestines          .........  289 

Influence  of  the  Nervous  System  on  Intestinal  Digestion    ....  290 


CHAPTEE  IX. 

ABSORPTION 291 

The  Lacteal  and  Lymphatic  Vessels  and  Glands 291 

Lymphatic  Glands 297 

Properties  of  Lymph  and  Chyle 301 

Absorption  by  the  Lacteal  Vessels        .         . 303 

Absorption  by  the  Lymphatic  Vessels 303 

Absorption  by  Blood-vessels          .         .         .         .         .....  305 


CONTENTS.  IX 

CHAPTER  X. 

PAGE 

ANIMAL  HEAT 309 

Variations  in  Bodily  Temperature 809 

'    Sources  of  Heat 311 

'    Loss  of  Heat 313 

Production  of  Heat 315 

Inhibitory  Heat-centre 316 

CHAPTER  XI. 

SECRETION 317 

SECRETING  MEMBRANES 319 

SEROUS  MEMBRANES 319 

Mucous  MEMBRANES    .                        321 

SECRETING  GLANDS 322 

PROCESS  OP  SECRETION 324 

CIRCUMSTANCES  INFLUENCING  SECRETION 326 

MAMMARY  GLANDS  AND  THEIR  SECRETION        ......  328 

CHEMICAL  COMPOSITION  OF  MILK 331 

CHAPTER  XII. 

THE  SKIN  AND  ITS  FUNCTIONS 333 

Structure  of  the  Skin 333 

Sudoriparous  Glands     ...........  337 

Sebaceous  Glands  ............  339 

Structure  of  Hair 339 

Structure  of  Nails 341 

Functions  of  the  Skin 342 

CHAPTER  XIII. 

THE  KIDNEYS  AND  URINE 347 

Structure  of  the  Kidneys 347 

Structure  of  the  Ureter  and  Urinary  Bladder 354 

The  Urine 355 

The  Secretion  of  Urine 365 

Micturition    .  373 


HAND-BOOK    OF    PHYSIOLOGY. 


CHAPTER  I. 

THE  GENERAL  AND  DISTINCTIVE  CHARACTERS  OF  LIVING 

BEINGS. 

HUMAX  PHYSIOLOGY  is  the  science  which  treats  of  the  \ife  of  man — • 
of  the  way  in  which  he  lives,  and  moves,  and  has  his  being.  It  teaches 
how  man  is  begotten  and  born;  how  he  attains  maturity;  and  how  he 
dies. 

Having,  then,  man  as  the  object  of  its  study,  it  is  unnecessary  to  speak 
here  of  the  laws  of  life  in  general,  and  the  means  by  which  they  are  car^ 
ried  out,  further  than  is  requisite  for  the  more  clear  understanding  of 
those  of  the  life  of  man  in  particular.  Yet  it  would  be  impossible  to 
understand  rightly  the  working  of  a  complex  machine  without  some 
knowledge  of  its  motive  power  in  the  simplest  form;  and  it  may  be  well 
to  see  first  what  are  the  so-called  essentials  of  life — those,  namely,  which 
are  manifested  by  all  living  beings  alike,  by  the  lowest  vegetable  and  the 
highest  animal — before  proceeding  to  the  consideration  of  the  structure 
and  endowments  of  the  organs  and  tissue  belonging  to  man. 

The  essentials  of  life  are  these, — Birth,  Growth  and  Development, 
Decline  and  Death. 

The  term  birth,  when  employed  in  this  general  sense  of  one  of  the 
conditions  essential  to  life,  without  reference  to  any  particular  kind  of 
living  being,  may  be  taken  to  mean,  separation  from  a  parent,  with  a 
greater  or  less  power  of  independent  life.  Taken  thus,  the  term, 
although  not  defining  any  particular  stage  in  development,  serves  well 
enough  for  the  expression  of  the  fact,  to  which  no  exception  has  yet  been 
proved  to  exist,  that  the  capacity  for  life  in  all  living  beings  is  obtained 
by  inheritance. 

Growth,  or  inherent  power  of  increasing  in  size,  although  essential 
to  our  idea  of  life,  is  not  confined  to  living  beings.  A  crystal  of  common 
salt,  or  of  any  other  similar  substance,  if  placed  under  appropriate  condi- 
VOL.  I.— 1. 


2  HAND-BOOK    OF    PHYSIOLOGY. 

tions  for  obtaining  fresh  material,  will  grow  in  a  fashion  as  definitely  char- 
acteristic and  as  easily  to  be  foretold  as  that  of  a  living  creature.  It  is, 
therefore,  necessary  to  explain  the  distinctions  which  exist  in  this  respect 
between  living  and  lifeless  structures;  for  the  manner  of  growth  in  the 
two  cases  is  widely  different. 

Differences  between  Living  and  Lifeless  Growth. — (1.)  The 
growth  of  a  crystal,  to  use  the  same  example  as  before,  takes  place  merely 
by  additions  to  its  outside;  the  new  matter  is  laid  on  particle  by  particle, 
and  layer  by  layer,  and,  when  once  laid  on,  it  remains  unchanged.  The 
growth  is  here  said  to  be  superficial.  In  a  living  structure,  on  the  other 
hand,  as,  for  example,  a  brain  or  a  muscle,  where  growth  occurs,  it  is  by 
addition  of  new  matter,  not  to  the  surface  only,  but  throughout  every 
part  of  the  mass;  the  growth  is  not  superficial,  but  interstitial. 

(2.)  All  living  structures  are  subject  to  constant  decay;  and  life  con- 
sists not,  as  once  supposed,  in  the  power  of  preventing  this  never-ceasing 
decay,  but  rather  in  making  up  for  the  loss  attendant  on  it  by  never- 
ceasing  repair.  Thus,  a  man's  body  is  not  composed  of  exactly  the  same 
particles  dayt after  day,  although  to  all  intents  he  remains  the  same  indi- 
vidual. Almost  every  part  is  changed  by  degrees;  but  the  change  is  so 
gradual,  and  the  renewal  of  that  which  is  lost  so  exact,  that  no  difference 
may  be  noticed,  except  at  long  intervals  of  time.  A  lifeless  structure, 
as  a  crystal,  is  subject  to  no  such  laws;  neither  decay  nor  repair  is  a 
necessary  condition,  of  its  existence.  That  which  is  true  of  structures 
which  never  had  to  do  with  life  is  true  also  with  respect  to  those  which, 
though  they  are  formed  by  living  parts,  are  not  themselves  alive.  Thus, 
an  oyster-shell  is  formed  by  the  living  animal  which  it  encloses,  but  it  is 
as  lifeless  as  any  other  mass  of  inorganic  matter;  and  in  accordance  with 
this  circumstance  its  growth  takes  place,  not  inter  stitially,  but  layer  by 
layer,  and  it  is  not  subject  to  the  constant  decay  and  reconstruction  which 
belong  to  the  living.  The  hair  and  nails  are  examples  of  the  same  fact. 

(3.)  In  connection  with  the  growth  of  lifeless  masses  there  is  no  alter- 
ation in  the  chemical  constitution  of  the  material  which  is  taken  up  and 
added  to  the  previously  existing  mass.  For  example,  when  a  crystal  of 
common  salt  grows  on  being  placed  in  a  fluid  which  contains  the  same 
material,  the  properties  of  the  salt  are  not  changed  by  being  taken  out  of 
the  liquid  by  the  crystal  and  added  to  its  surface  in  a  solid  form.  But 
the  case  is  essentially  different  in  living  beings,  both  animal  and  vegeta- 
ble. A  plant,  like  a  crystal,  can  only  grow  when  fresh  material  is  pre- 
sented to  it;  and  this  is  absorbed  by  its  leaves  and  roots;  and  animals, 
for  the  same  purpose  of  getting  new  matter  for  growth  and  nutrition, 
take  food  into  their  stomachs.  But  in  both  these  cases  the  materials  are 
much  altered  before  they  are  finally  assimilated  by  the  structures  they 
are  destined  to  nourish. 

(4.)  The  growth  of  all  living  things  has  a  definite  limit,  and  the  Li\v 


DISTINCTIVE    CHAKACTEKS    OF    LIVING    BEIXGS.  '     3 

governs  this  limitation  of  increase  in  size  is  so  invariable  that  we 
should  be  as  much  astonished  to  find  an  individual  plant  or  animal  with- 
out limit  as  to  growth  as  without  limit  to  life. 

Development  is  as  constant  an  accompaniment  of  life  as  growth.  The 
term  is  used  to  indicate  that  change  to  which,  before  maturity,  all  living 
parts  are  constantly  subject,  and  by  which  they  are  made  more  and  more 
capable  of  performing  their  several  functions.  For  example,  a  full-grown 
man  is  not  merely  a  magnified  child ;  his  tissues  and  organs  have  not  only 
grown,  or  increased  in  size,  they  have  also  developed,  or  become  better  in 
quality. 

;No  very  accurate  limit  can  be  drawn  between  the  end  of  development 
and  the  beginning  of  decline;  and  the  two  processes  may  be  often  seen 
together  in  the  same  individual.  But  after  a  time  all  parts  alike  share 
in  the  tendency  to  degeneration,  and  this  is  at  length  succeeded  by  death. 

Differences  between  Plants  and  Animals.— It  has  been  already 
said  that  the  essential  features  of  life  are  the  same  in  all  living  things; 
in  other  words,  in  the  members  of  both  the  animal  and  vegetable  king- 
doms. It  may  be  wrell  to  notice  briefly  the  distinctions  which  exist  be- 
tween the  members  of  these  two  kingdoms.  It  may  seem,  indeed,  a 
strange  notion  that  it  is  possible  to  confound  vegetables  with  animals, 
but  it  is  true  with  respect  to  the  lowest  of  them,  in  which  but  little  is 
manifested  beyond  the  essentials  of  life,  which  are  the  same  in  both. 

(1.)  Perhaps  the  most  essential  distinction  is  the  presence  or  absence 
of  power  to  live  upon  inorganic  material.  By  means  of  their  green  color- 
ing matter,  chlorophyl — a  substance  almost  exclusively  confined  to  the 
vegetable  kingdom,  plants  are  capable  of  decomposing  the  carbonic  acid, 
ammonia,  and  water,  which  they  absorb  by  their  leaves  and  roots,  and 
thus  utilizing  them  as  food.  The  result  of  this  chemical  action,  which 
occurs  only  under  the  influence  of  light,  is,  so  far  as  the  carbonic  acid  is 
concerned,  the  fixation  of  carbon  in  the  plant  structures  and  the  exhala- 
tion of  oxygen.  Animals  are  incapable  of  thus  using  inorganic  matter, 
and  never  exhale  oxygen  as  a  product  of  decomposition. 

The  power  of  living  upon  organic  as  well  as  inorganic  matter  is  less 
decisive  of  an  animal  nature;  inasmuch  as  fungi  and  some  other  plants 
derive  their  nourishment  in  part  from  the  former  source. 

(2.)  There  is,  commonly,  a  marked  difference  in  general  chemical 
composition  between  vegetables  and  animals,  even  in  their  lowest  forms; 
for  while  the  former  consist  mainly  of  cellulose,  a  substance  closely  allied 
to  starch  and  containing  carbon,  hydrogen,  and  oxygen  only,  the  latter 
are  composed  in  great  part  of  the  three  elements  just  named,  together 
with  a  fourth,  nitrogen;  the  chief  proximate  principles  formed  from 
these  being  identical,  or  nearly  so,  with  albumen.  It  must  not  be  sup- 
posed, however,  that  either  of  these  typical  compounds  alone,  with  its 
allies,  is  confined  to  one  kingdom  of  nature.  Nitrogenous  compounds 


4  HAND-BOOK    OF    PHYSIOLOGY. 

are  freely  produced  in  vegetable  structures,  although  they  form  a  very 
much  smaller  proportion  of  the  whole  organism  than  cellulose  or  starch. 
And  while  the  presence  of  the  latter  in  animals  is  much  more  rare  than 
is  that  of  the  former  in  vegetables,  there  are  many  animals  in  which 
traces  of  it  may  be  discovered,  and  some,  the  Ascidians,  in  which  it  is 
found  in  cpnsiderable  quantity. 

(3. )  Inherent  power  of  movement  is  a  quality  which  we  so  commonly 
consider  an  essential  indication  of  animal  nature,  that  it  is  difficult  at 
first  to  conceive  it  existing  in  any  other.  The  capability  of  simple  motion 
is  now  known,  however,  to  exist  in  so  many  vegetable  forms,  that  it  can 
no  longer  be  held  as  an  essential  distinction  between  them  and  animals, 
and  ceases  to  be  a  mark  by  which  the  one  can  be  distinguished  from  the 
other.  Thus  the  zoospores  of  many  of  the  Cryptogamia  exhibit  ciliary 
or  amoeboid  movements  (p.  8)  of  a  like  kind  to  those  seen  in  animalcules; 
and  even  among  the  higher  orders  of  plants,  many,  e.  g.,  Dioncea  Mus- 
cipula  (Venus's  fly -trap),  and  Mimosa  Sensitiva  (Sensitive  plant),  exhibit 
such  motion,  either  at  regular  times,  or  on  the  application  of  external 
irritation,  as  might  lead  one,  were  this  fact  taken  by  itself,  to  regard 
them  as  sentient  beings.  Inherent  power  of  movement,  then,  although 
especially  characteristic  of  animal  nature,  is,  when  taken  by  itself,  no 
proof  of  it. 

(4.)  The  presence  of  a  digestive  canal  is  a  very  general  mark  by 
which  an  animal  can  be  distinguished  from  a  vegetable.  But  the  lowest 
animals  are  surrounded  by  material  that  they  can  take  as  food,  as  a  plant 
is  surrounded  by  an  atmosphere  that  it  can  use  in  like  manner.  And 
every  part  of  their  body  being  adapted  to  absorb  and  digest,  they  have 
no  need  of  a  special  receptacle  for  nutrient  matter,  and  accordingly  have 
no  digestive  canal.  This  distinction  then  is  not  a  cardinal  one. 

It  would  be  tedious  as  well  as  unnecessary  to  enumerate  the  chief  dis- 
tinctions between  the  more  highly  developed  animals  a*nd  vegetables. 
They  are  sufficiently  apparent.  It  is  necessary  to  compare,  side  by  side, 
the  lowest  members  of  the  two  kingdoms,  in  order  to  understand  rightly 
how  faint  are  the  boundaries  between  them. 


CHAPTER  II. 

STRUCTURAL  BASIS  OF  THE  HUMAN  BODY. 

BY  dissection,  the  human  body  can  be  proved  to  consist  of  various  dis- 
similar parts,  bones,  muscles,  brain,  heart,  lungs,  intestines,  etc.,  while, 
on  more  minute  examination,  these  are  found  to  be  composed  of  different 
tissues,  such  as  the  connective,  epithelial,  nervous,  muscular,  and  the 
like. 

Cells. — Embryology  teaches  us  that  all  this  complex  organization  has 
been  developed  from  a  microscopic  body  about  y-J-0-  in.  in  diameter 
(ovum),  which  consists  of  a  spherical  mass  of  jelly-like  matter  enclosing 
a  smaller  spherical  body  (germinal  vesicle).  Further,  each  individual 
tissue  can  be  shown  largely  to  consist  of  bodies  essentially  similar  to  an 
ovum,  though  often  differing  from  it  very  widely  in  external  form.  They 
are  termed  cells :  and  it  must  be  at  once  evident  that  a  correct  knowledge 
of  the  nature  and  activities  of  the  cell  forms  the  very  foundation  of 
physiology. 

Cells  are,  in  fact,  physiological  no  less  than  histological  units. 

The  prime  importance  of  the  cell  as  an  element  of  structure  was  first 
established  by  the  researches  of  Schleiden,  and  his  conclusions,  drawn 
from  the  study  of  vegetable  histology,  were  at  once  extended  by  Schwann 
to  the  animal  kingdom.  The  earlier  observers  defined  a  cell  as  a  more  or 
less  spherical  body  limited  by  a  membrane,  and  containing  a  smaller  body 
termed  a  nucleus,  which  in  its  turn  encloses  one  or  more  nucleoli.  Such 
a  definition  applied  admirably  to  most  vegetable  cells,  but  the  more 
extended  investigation  of  animal  tissues  soon  showed  that  in  many  cases 
no  limiting  membrane  or  cell-wall  could  be  demonstrated. 

The  presence  or  absence  of  a  cell- wall,  therefore,  was  now  regarded  as 
quite  a  secondary  matter,  while  at  the  same  time  the  cell-substance  came 
gradually  to  be  recognized  as  of  primary  importance.  Many  of  the  lower 
forms  of  animal  life,  e.g.,  the  Rhizopoda,were  found  to  consist  almost  entire- 
ly of  matter  very  similar  in  appearance  and  chemical  composition  to  the 
cell-substance  of  higher  forms:  and  this  from  its  chemical  resemblance  to 
flesh  was  termed  Sarcode  by  Dujardin.  When  recognized  in  vegetable 
cells  it  was  called  Protoplasm  by  Mulder,  while  Remak  applied  the  same 
name  to  the  substance  of  animal  cells.  As  the  presumed  formative  mat- 
ter in  animal  tissues  it  was  termed  Blastema,  and  in  the  belief  that, 
wherever  found,  it  alone  of  all  substances  has  to  do  with  generation  and 


6  HAND-BOOK    OF    PHYSIOLOGY. 

nutrition,  Beale  has  named  it  Germinal  matter  or  Bioplasm.  Of  these 
terms  the  one  most  in  vogue  at  the  present  day  is  Protoplasm,  and  inas- 
much as  all  life,  both  in  the  animal  and  vegetable  kingdoms,  is  associated 
with  protoplasm,  we  are  justified  in  describing  it,  with  Huxley,  as  the 
"physical  basis  of  life." 

A  cell  may  now  be  defined  as  a  nucleated  mass  of  protoplasm,1  of 
microscopic  size,  which  possesses  sufficient  individuality  to  have  a  life- 
history  of  its  own.  Each  cell  goes  through  the  same  cycle  of  changes 
as  the  whole  organism,  though  doubtless  in  a  much  shorter  time.  Begin- 
ning with  its  origin  from  some  pre-existing  cell,  it  grows,  produces  other 
cells,  and  finally  dies.  It  is  true  that  several  lower  forms  of  life  consist  of 
non-nucleated  protoplasm,  but  the  above  definition  holds  good  for  all 
the  higher  plants  and  animals. 

Hence  a  summary  of  the  manifestations  of  cell-life  is  really  an  account 
of  the  vital  activities  of  protoplasm. 

Protoplasm. — Physical  characters. — Physically,  protoplasm  is  viscid, 
varying  in  consistency  from  semi-fluid  to  stronglyc  oherent.  Chemical 
characters.  — Chemically,  living  protoplasm  is  an  extremely  unstable  albu- 
minoid substance,  insoluble  in  water.  It  is  neutral  or  weakly  alkaline  in 
reaction.  It  undergoes  heat  stiffening  or  coagulation  at  about  130°F. 
(54'5°C.),  and  hence  no  organism  can  live  when  its  own  temperature  is 
raised  beyond  this  point,  though,  of  course,  many  can  exist  for  a  time  in 
a  much  hotter  atmosphere,  since  they  possess  the  means  of  regulating 
their  own  temperature.  Besides  the  coagulation  produced  by  heat,  pro- 
toplasm is  coagulated  by  all  the  reagents  which  produce  this  change  in 
albumen.  If  not-living  protoplasm  be  subjected  to  chemical  analysis  it 
is  found  to  be  made  up  of  numerous  bodies2  besides  albumen,  e.g.,  of  gly- 
cogen,  lecithin,  salts  and  water,  so  that  if  living  protoplasm  be,  as  some 
believe,  an  independent  chemical  body,  when  it  no  longer  possesses  life, 
it  undergoes  a  disintegration  which  is  accompanied  by  the  appearance  of 
these  new  chemical  substances.  When  it  is  examined  under  the  micro- 
scope two  varieties  of  protoplasm  are  recognized — the  hyaline,  and  the 
granular.  Both  are  alike  transparent,  but  the  former  is  perfectly  homo- 
geneous, while  the  latter  (the  more  common  variety)  contains  small  gran- 
ules or  molecules  of  various  sizes  and  shapes.  Globules  of  watery  fluid 
are  also  sometimes  found  in  protoplasm;  they  look  like  clear  spaces  in  it, 
and  are  hence  called  vacuoles. 

Vital  or  Physiological  characters. — These  may  be  conveniently  treated 
under  the  three  heads  of — I.  Motion;  II.  Nutrition;  and  III.  Repro- 
duction. 


1  In  the  Luman  body  the  cells  range  from  the  red  blood-cell  (-g^Vo"  in.)  to  the  gang- 
lion-cell (y^-)  in. 

2  For  an  account  of  which,  reference  should  be  made  to  the  Appendix. 


STRUCTURAL    BASIS    OF    THE    HUMAN    BODY. 


I.  Motion.  —  It  is  probable  that  the  protoplasm  of  all  cells  is  capable 
at  some  time  of  exhibiting  movement;  at  any  rate  this  phenomenon, 
which  not  long  ago  was  regarded  as  quite  a  curiosity,  has  been  recently 
observed  in  cells  of  •  many  different  kinds.  It  maybe  readily  studied  in 
the  Amoebae,  in  the  colorless  blood  -cells  of  all  vertebrata,  in  the  branched 
cornea-cells  of  the  frog,  in  the  hairs  of  the  stinging-nettle  and  Trades- 
cunt  ia.  arid  the  cells  of  Vallisneria  and  Chara. 

These  motions  may  be  divided  into  two  classes  —  (a)  Fluent  and  (b) 
Ciliary. 

Another  variety  —  the  molecular  or  vibratory  —  has  also  been  classed  by 
some  observers  as  vital,  but  it  seems  exceedingly  probable  that  it  is 
nothing  more  than  the  well-known  "Brownian"  molecular  movement,  a 
purely  mechanical  phenomenon  which  may  be  observed  in  any  minute 
particles,  e.g.,  of  gamboge,  suspended  in  a  fluid  of  suitable  density,  such 
as  water. 

Such  particles  are  seen  to  oscillate  rapidly  to  and  fro,  and  not  to  pro- 
gress in  any  definite  direction. 

(a.)  Fluent.  —  This  movement  of  protoplasm  is  rendered  perceptible 
(1)  by  the  motion  of  the  granules,  which  are  nearly  always  imbedded  in 
it,  and  (2)  by  changes  in  the  outline  of 
its  mass. 

If  part  of  a  hair  of  Tradescantia 
(Fig.  1)  be  viewed  under  a  high  magni- 
fying power,  streams  of  protoplasm  con- 
taining crowds  of  granules  hurrying 
along,  like  the  foot  passengers  in  a  busy 
street,  are  seen  flowing  steadily  in  defi- 
nite directions,  some  coursing  round 

the    film  Which  lilies  the  Ulterior  Of   the 

,,         , 
Cell-wall,  and   Others   liowmo;  toward 


Or 


FIG.  1.—  Cell  of  Tfcidescantia  drawn  at 
successive  intervals  of  two  minutes.  The 
cell-contents  consist  of  a  central  mass  con- 
nected  by  many  irregular  processes  to  a 
peripheral  film:  the  whole  forms  a  vacuo- 


.  ,         .  - 

from     the    irregular    maSS    in    the     lated  mass  of  protoplasm,  which  is  continu- 
„  ,  ,  ..  ,,  ally  changing  its  shape.    (Schofield.) 

centre  of  the  cell-cavity.    Many  of  these 

streams  of   protoplasm  run  together  into  larger  ones,  and  are  lost  in 

the  central  mass,  and  thus  ceaseless  variations  of  form  are  produced. 

In  the  Amoeba,  a  minute  animal  consisting  of  a  shapeless  and  struc- 
tureless mass  of  sarcode,  an  irregular  mass  of  protoplasm  is  gradually 
thrust  out  from  the  main  body  and  retracted:  a  second  mass  is  then  pro- 
truded in  another  direction,  and  gradually  the  whole  protoplasmic  sub- 
stance is,  as  it  were,  drawn  into  it.  The  Amoeba  thus  comes  to  occupy  a 
new  position,  and  when  this  is  repeated  several  times  we  have  locomotion 
in  a  definite  direction,  together  with  a  continual  change  of  form.  These 
movements  when  observed  in  other  cells,  such  as  the  colorless  blood- 
corpuscles  of  higher  animals  (Fig.  2)  are  hence  termed  amoeboid. 

Colorless   blood-corpuscles   were   first  observed   to   migrate,  i.e.,  pass 


HAND-BOOK    OF    PHYSIOLOGY. 

through  the  walls  of  the  blood-vessels  (p.  159),  by  Waller,  whose  obser- 
vations were  confirmed  and  extended  to  connective  tissue  corpuscles  by 
the  researches  of  Recklirighausen,  Cohnheim,  and  others,  and  thus  the 
phenomenon  of  migration  has  been  proved  to  play  an  important  part  in 
many  normal,  and  pathological  processes,  especially  in  that  of  inflam- 
mation. 

This  amoeboid  movement  enables  many  of  the  lower  animals  to  capture 
their  prey,  which  they  accomplish  by  simply  flowing  round  and  enclosing  it. 

The  remarkable  motions  of  pigment-granules  observed  in  the  branched 
pigment-cells  of  the  frog's  skin  by  Lister  are  probably  due  to  amoeboid 
movement.  These  granules  are  seen  at  one  time  distributed  uniformly 
through  the  body  and  branched  processes  of  the  cell,  while  under  the 
action  of  various  stimuli  (e.g.,  light  and  electricity)  they  collect  in  the 
central  mass,  leaving  the  branches  quite  colorless. 

(b.)  Ciliary  action  must  be  regarded  as  only  a  special  variety  of  the 
general  motion  with  which  all  protoplasm  is  endowed. 

The  grounds  for  this  view  are  the  following:  In  the  case  of  the  Infu- 
soria, which  move  by  the  vibration  of  cilia  (microscopic  hair-like  processes 
projecting  from  the  surface  of  their  bodies)  it  has  been  proved  that  these 
are  simply  processes  of  their  protoplasm  protruding  through  pores  of  the 


FIG.  2.— Human  colorless  blood-corpuscle,  showing  its  successive  changes  of  outline  within  ten 
minutes  when  kept  moist  on  a  warm  stage.    (Schofield.) 

investing  membrane,  like  the  oars  of  a  galley,  or  the  head  and  legs  of  a 
tortoise  from  its  shell:  certain  reagents  cause  them  to  be  partially  re- 
tracted. Moreover,  in  some  cases  cilia  have  been  observed  to  develop  from, 
and  in  others  to  be  transformed  into,  amoeboid  processes. 

The  movements  of  protoplasm  can  be  very  largely  modified  or  even 
suspended  by  external  conditions,  of  which  the  following  are  the  most 
important. 

1.  Changes  of  temperature. — Moderate  heat  acts  as  a  stimulant  this 
is  readily  observed  in  the  activity  of  the  movements  of  a  human  colorless 
blood-corpuscle  when  placed  under  conditions  in  which  its  normal  tem- 
perature and  moisture  are  preserved.     Extremes  of  heat  and  cold  stop  the 
motions  entirely. 

2.  Mechanical  stimuli. — When  gently  squeezed  between  a  cover  and 
object  glass  under  proper  conditions,  a  colorless  blood-corpuscle  is  stimu- 
lated to  active  amoeboid  movement. 

3.  Nerve  influence. — By  stimulation  of  the  nerves  of  the  frog's  cornea, 
contraction  of  certain  of  its  branched  cells  has  been  produced. 

4.  Chemical  stimuli. — Water  generally  stops  amoeboid  movement,  and 
by  imbibition  causes  great  swelling  and  finally  bursting  of  the  cells. 


STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.  9 

In  some  cases,  however,  (myxomycetes)  protoplasm  can  be  almost 
entirely  dried  up,  and  is  yet  capable  of  renewing  its  motions  when  again 
moistened. 

Dilute  salt-solution  and  many  dilute  acids  and  alkalies,  stimulate  the 
movements  temporarily. 

Ciliary  movement  is  suspended  in  an  .atmosphere  of  hydrogen  or  car- 
bonic acid,  and  resumed  on  the  admission  of  air  or  oxygen. 

5.  Electrical. — Weak  currents  stimulate  the  movement,  while  strong 
currents  cause  the  corpuscles  to  assume  a  spherical  form  and  to  become 
motionless. 

II.  Nutrition. — The  nutrition  of  cells  will  be  more  appropriately 
described  in  the  chapters  on  Secretion  and  Nutrition. 

Before  describing  the  Reproduction  of  cells  it  will  be  necessary  to  con- 
sider their  structure  more  at  length. 

Minute  Structure  of  Cells. — (a.)  Cell-wall. — We  have  seen  (p.  5) 
that  the  presence  of  a  limiting-membrane  is  no  essential  part  of  the  defini- 
tio7i  of  a  cell. 

In  nearly  all  cells  the  outer  layer  of  the  protoplasm  attains  a  firmer 
consistency  than  the  deeper  portions:  the  individuality  of  the  cell  be- 
coming more  and  more  clearly  marked  as  this  cortical  layer  becomes  more 
and  more  differentiated  from  the  deeper  portions  of  cell-substance.  Side 
by  side  with  this  physical,  there  is  a  gradual  chemical  differentiation,  till 
at  length,  as  in  the  case  of  the  fat-cells,  we  have  a  definite  limiting-mem- 
brane differing  chemically  as  well  as  physically  from  the  cell-contents, 
and  remaining  as  a  shriveled-up  bladder  when  they  have  been  removed. 
Such  a  membrane  is  transparent  and  structureless,  flexible,  and  per- 
meable to  fluids. 

The  cell-substance  can,  therefore,  still  be  nourished  by  imbibition 
through  the  cell- wall.  In  many  cases  (especially  in  fat)  a  membrane  of 
some  toughness  is  absolutely  necessary  to  give  to  the  tissue  the  requisite 
consistency.  When  these  membranes  attain  a  certain  degree  of  thickness 
and  independence  they  are  termed  capsules:  as  examples,  we  may  cite  the 
capsules  of  cartilage-cells,  and  the  thick,  tough  envelope  of  the  ovum 
termed  the  "primitive  chorion." 

(b.)  Cell  contents. — In  accordance  with  their  respective  ages,  positions, 
and  functions,  the  contents  of  cells  are  very  varied. 

The  original  protoplasmic  substance  may  undergo  many  transforma- 
tions; thus,  in  fat-cells  we  may  have  oil,  or  fatty  crystals,  occupying 
nearly  the  whole  cell-cavity:  in  pigment-cells  we  find  granules  of  pig- 
ment; in  the  various  gland-cells  the  elements  of  their  secretions. 
Moreover,  the  original  protoplasmic  contents  of  the  cell  may  undergo  a 
gradual  chemical  change  with  advancing  age;  thus  the  protoplasmic  cell- 
substance  of  the  deeper  layers  of  the  epidermis  becomes  gradually  con- 
verted into  keratin  as  the  cell  approaches  the  surface.  So,  too,  the  orig- 


10  HAND-BOOK    OF    PHYSIOLOGY. 

inal  protoplasm  of  the  embryonic  blood-cells  is  replaced  by  the  haemo- 
globin of  the  mature  colored  blood-corpuscle. 

The  minute  structure  of  cells  has  lately  been  made  the  subject  of  care- 
ful investigation,  and  what  was  once  regarded  as  homogeneous  proto- 
plasm with  a  few  scattered  granules,  has  been  stated  to  be  an  exceedingly 
complex  structure.  In  colorless  blood-corpuscles,  epithelial  cells,  con- 
nective tissue  corpuscles,  nerve-cells,  and  many  other  varieties  of  cells, 
an  intracellular  network  of  very  fine  fibrils,  the  meshes  of  which  are 
occupied  by  a  hyaline  interstitial  substance,  has  been  demonstrated 
(Heitzmann's  network)  (Fig.  3).  At  the  nodes,  where  the  fibrils  cross, 
are  little  swellings,  and  these  are  the  objects  described  as  granules  by 
the  older  observers:  but  in  some  cells,  e.g.,  colorless  blood  corpuscles, 
there  are  real  granules,  which  appear  to  be  quite  free  and  unconnected 
with  the  intra-cellular  network. 

(c. )  Nucleus. — Nuclei  (Fig.  3)  were  first  pointed  out  in  the  year  1833, 
by  Robert  Brown,  who  observed  them  in  vegetable  cells.  They  are  either 


FIG.  3.  —  (A).  Colorless  blood-corpuscle  showing  intra-cellular  network  of  Heitzmann,  and  two 
nuclei  with  intra-nuclear  network.  (Klein  and  Noble  Smith.) 

(B.)  Colored  blood-corpuscle  of  newt  showing  intra-cellular  network  of  fibrils  (Heitzmann).  Also 
oval  nucleus  composeAf  limiting-membrane  and  fine  intra-nuclear  network  of  fibrils.  X  800.  (Klein 
and  Noble  Smith.) 

small  transparent  vesicular  bodies  containing  one  or  more  smaller  particles 
(nucleoli),  or  they  are  semi-solid  masses  of  protoplasm  always  in  the 
resting  condition  bounded  by  a  well-defined  envelope.  In  their  relation 
to  the  life  of  the  cell  they  are  certainly  hardly  second  in  importance  to 
the  protoplasm  itself,  and  thus  Beale  is  fully  justified  in  comprising  both 
under  the  term  "germinal  matter."  They  exhibit  their  vitality  by  ini- 
tiating the  process  of  division  of  the  cell  into  two  or  more  cells  (fission) 
by  first  themselves  dividing.  Distinct  observations  have  been  made  show- 
ing that  spontaneous  changes  of  form  may  occur  in  nuclei  as  also  in  nu- 
cleoli. 

Histologists  have  long  recognized  nuclei  by  two  important  charac- 
ters:— 

(1.)  Their  power  of  resisting  the  action  of  various  acids  and  alkalies, 
particularly  acetic  acid,  by  which  their  outline  is  more  clearly  defined, 
and  they  are  rendered  more  easily  visible.  This  indicates  some  chemical 


STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.  11 

difference  between  the  protoplasm  of  the  cell  and  nuclei,  as  the  former  is 
destroyed  by  these  reagents. 

(2. )  Their  quality  of  staining  in  solutions  of  carmine,  haematoxylin, 
etc.  Nuclei  'are  most  commonly  oval  or  round,  and  do  not  generally 
conform  to  the  diverse  shapes  of  the  cells;  they  are  altogether  less  varia- 
ble elements  than  cells,  even  in  regard  to .  size,  of  which  fact  one  may  see 
a  good  example  in  the  uniformity  of  the  nuclei  in  cells  so  multiform  as 
those  of  epithelium.  But  sometimes  nuclei  appear  to  occupy  the  whole 
of  the  cell,  as  is  the  case  in  the  lymph  corpuscles  of  lymphatic  glands 
and  in  some  small  nerve  cells. 

Tlieir  position  in  the  cell  is  very  variable.  In  many  cells,  especially 
where  active  growth  is  progressing,  two  or  more  nuclei  are  present. 

The  nuclei  of  many  cells  have  been  shown  to  contain  a  fine  intra- 
nuclear network  in  every  respect  similar  to  that  described  above  as  intra- 
cellular  (Fig.  3),  the  interstices  of  which  are  occupied  by  semi-fluid  pro- 
toplasm. 

III.  Reproduction.— The  life  of  individual  cells  is  probably  very 
short  in  comparison  with  that  of  the  organism  they  compose:  and  their 
constant  decay  and  death  necessitate  constant  reproduction.  The  mode 
in  which  this§takes  place  has  long  been  the  subject  of  great  controversy. 

In  the'  case  of  plants,  all  of  whose  tissues  are  either  cellular  or  com- 
posed of  cells  which  are  modified  or  have  coalesced  in  various  ways,  the 
theory  that  all  new  cells  are  derived  from  pre-existing  ones  was  early  ad- 
vanced and  very  generally  accepted.  But  in  the  case  of  animal  tissues 
Scliwann  and  others  maintained  a  theory  of  spontaneous  or  free  cell  for- 
mation. 

According  to  this  view  a  minute  corpuscle  (the  future  nucleolus) 
springs  up  spontaneously  in  a  structureless  substance  (blaslbma)  very  much 
as  a  crystal  is  formed  in  a  solution.  This  nucleolus  attracts  the  surround- 
ing molecules  of  matter  to  form  the  nucleus,  and  by  a  repetition  of  the 
process  the  substance  and  wall  are  produced. 

This  theory,  once  almost  universally  current,  was  first  disputed  and 
finally  overthrown  by  Remak  and  Virchow,  whose  researches  established 
the  truth  expressed  in  the  words  "Omnis  celiula  e  cellula." 

It  will  be  seen  that  this  view  is  in  strict  accordance  with  the  truth 
established  much  earlier  in  Vegetable  Histology  that  every  cell  is  de- 
scended from  some  pre-existing  (mother-)  cell.  This  derivation  of  cells 
from  cells  takes  place  by  (1)  gemmation,  or  (2)  fission  or  division. 

(1.)  Gemmation. — This  method  has  not  been  observed  in  the  human 
body  or  the  higher  animals,  and  therefore  requires  but  a  passing  notice. 
It  consists  essentially  in  the  budding  off  and  separating  of  a  portion  of 
the  parent  cell. 

(2.)  Fixxion  or  Division. — As  examples  of  reproduction  by  fission,  we 
may  select  the  ovum,  the  blood  coll,  and  cartilage  cells. 


12  HAND-BOOK    OF    PHYSIOLOGY. 

In  the  frog's  ovum  (in  which  the  process  can  be  most  readily  ob- 
served) after  fertilization  has  taken  place,  there  is  first  some  amoeboid 
movement,  the  oscillation  gradually  increasing  until  a  permanent  dimple 
appears,  which  gradually  extends  into  a  furrow  running  completely  round 
the  spherical  ovum,  and  deepening  until  the  entire  yelk-rnass  is  divided 
into  two  hemispheres  of  protoplasm  each  containing  a  nucleus  (Fig.  4,  b). 
This  process  being  repeated  by  the  formation  of  a  second  furrow  at  right 
angles  to  the  first,  we  have  four  cells  produced  (c):  this  subdivision  is 


FIG.  4.— Diagram  of  an  ovum  (a)  undergoing  segmentation.  In  (6)  it  has  divided  into  two;  in  (c) 
into  four;  in  (d)  the  process  has  ended  in  the  production  of  the  so-called  u  mulberry  mass."  (Frey.) 

carried  on  till  the  ovum  has  been  diyided  by  segmentation  into  a  mass 
of  cells  (mulberry-mass)  (d)  out  of  which  the  embryo  is  developed. 

Segmentation  is  the  first  step  in  the  development  of  most  animals, 
and  doubtless  takes  place  in  man. 

Multiplication  by  fission  has  been  observed  in  the  colorless  blood-cells 
of  many  animals.  In  some  cases  (Fig.  5),  the  process  has  been  seen  to 
commence  with  the  nucleolus  which  divides  within  the  nucleus.  The 
nucleus  then  elongates,  and  soon  a  well-marked  constriction  occurs,  ren- 
dering it  hour-glass  shaped,  till  finally  it  is  separated  into  two  parts, 
which  gradually  recede  from  each  other:  the  same  process  is  repeated  in 
the  cell- substance,  and  at  length  we  have  two  cells  produced  which  by 

/$)       <S        (•) 

(sf      ®      (•) 

Fio.  5.— Blood-corpuscle  from  a  young  deer  embryo,  multiplying  by  fission.    (Frey.) 

rapid  growth  soon  attain  the  size  of  the  parent  cell  (direct  division).  In 
some  cases  there  is  a  primary  fission  into  three  instead  of  the  usual  two 
cells. 

In  cartilage  (Fig.  6),  a  process  essentially  similar  occurs,  with  the  ex- 
ception that  (as  in  the  ovum)  the  cells  produced  by  fission  remain  in  the 
original  capsule,  and  in  their  turn  undergo  division,  so  that  a  large  num- 
ber of  cells  are  sometimes  observed  within  a  common  envelope.  This 
process  of  fission  within  a  capsule  has  been  by  some  described  as  a  separate 
method,  under  the  title  i 'endogenous  fission,"  but  there  seems  to  be  no 
sufficient  reason  for  drawing  such  a  distinction. 

It  is  important  to  observe  that  fission  is  often  accomplished  with  great 
rapidity,  the  whole  process  occupying  but  a  few  minutes,  hence  the  com- 
parative rarity  with  which  cells  are  seen  in  the  act  of  dividing. 


STRUCTURAL    BASIS    OF    THE    HUMAN    BODY. 


13 


Indirect  cell  division. — In  certain  and  numerous  cases  the  division  of 
cells  does  not  take  place  by  the  simple  constriction  of  their  nuclei  and 
surrounding  protoplasm  into  two  parts  as  above  described  (direct  division), 
but  is  preceded  by  complicated  changes  in  their  nuclei  (karyokinesis). 


FIG.  6.— Diagram  of  a  cartilage  cell  undergoing  fission  within  its  capsule.  The  process  of  divi- 
sion is  represented  as  commencing  in  the  nucleolus,  extending  to  the  nucleus,  and  at  length  involving 
the  body  of  the  cell.  (Frey.) 

These  changes  consist  in  a  gradual  re-arrangement  of  the  intranuclear  net- 
work of  each  nucleus,  until  two  nuclei  are  formed  similar  in  all  respects 
to  the  original  one.  The  nucleus  in  a  resting  condition,  i.e.,  before  any 
changes  preceding  division  occur,  consists  of  a  very  close  meshwork  of 
fibrils,  which  stain  deeply  in  carmine,  imbedded  in  protoplasm,  which 
does  not  possess  this  property,  the  whole  nucleus  being  contained  in  an 
envelope.  The  first  change  consists  of  a  slight  enlargement,  the  disap- 
pearance of  the  envelope,  and  the  increased  definition  and  thickness  of 


FIG.  ?.— Karyokinesis.  A,  ordinary  nucleus  of  a  columnar  epithelial  cell:  B,  c,  the  same  nucleus  in 
the  stage  of  convolution;  D,  the  wreath  or  rosette  form;  E,  the  aster  or  single  star:  F,  a  nuclear  spin- 
dle from  the  Descemet's  endothelium  of  the  frog's  cornea:  G,  H,  i,  diaster;  K,  two  daughter  nuclei. 
(Klein.) 

the  nuclear  fibrils,  which  are  also  more  separated  than  they  were  and  stain 
better.  This  is  the  stage  of  convolution  (Fig.  7,  B,  c).  The  next  step  in 
the  process  is  the  arrangement  of  the  fibrils  into  some  definite  figure  by 
an  alternate  looping  in  and  out  around  a  central  space,  by  which  means 


14  HAND-BOOK  OF  PHYSIOLOGY. 

the  rosette  or  wreath  stage  (Fig.  7,  D)  is  reached.  The  loops  of  the  rosette 
next  become  divided  at  the  periphery,  and  their  central  points  become 
more  angular,  so  that  the  fibrils,  divided  into  portions  of  about  equal 
length,  are,  as  it  were,  doubled  at  an  acute  angle,  and  radiate  V-shaped 
from  the  centre,  forming  a  star  (aster)  or  wheel  (Fig.  7,  E),  or  perhaps 
from  two  centres,  in  which  case  a  double  star  (diaster)  results  (Fig.  7,  G, 
H,  and  i).  After  remaining  almost  unchanged  for  some  time,  the 
V-shaped  fibres  being  first  re-arranged  in  the  centre,  side  by  side  (angle 
outward),  tend  to  separate  into  two  bundles,  which  gradually  assume  posi- 
tion at  either  pole.  From  these  groups  of  fibrils  the  two  nuclei  of  the 
new  cells  are  formed  (daughter  nuclei)  (Fig.  7,  K),  and  the  changes  they 
pass  through  before  reaching  the  resting  condition  are  exactly  those 
through  which  the  original  nucleus  (mother  nucleus)  has  gone,  but  in  a 
reverse  order,  viz.,  the  star,  the  rosette,  and  the  convolution.  During 
or  shortly  after  the  formation  of  the  daughter  nuclei  the  cell  itself  be- 
comes constricted,  and  then  divides  in  a  line  about  midway  between  them. 

Functions  of  Cells. — The  functions  of  cells  are  almost  infinitely  varied 
and  make  up  nearly  the  whole  of  Physiology.  They  will  be  more  appro- 
priately considered  in  the  chapters  treating  of  the  several  organs  and  sys- 
tems of  organs  which  the  cells  compose. 

Decay  and  Death  of  Cells. — There  are  two  chief  ways  in  which  the 
comparatively  brief  existence  of  cells  is  brought  to  an  end.  (1)  Mechani- 
cal abrasion,  (2)  Chemical  transformation. 

1.  The  various  epithelia  furnish  abundant  examples  of  mechanical 
abrasion.     As  it  approaches  the  free  surface  the  cell  becomes  more  and 
more  flattened  and  scaly  in  form  and  more  horny  in  consistence,  till  at 
length  it  is  simply  rubbed  off.     Hence  we  find  epithelial  cells  in  the 
mucus  of  the  mouth,  intestine,  and  genito-urinary  tract. 

2.  In  the  case  of  chemical  transformation  the  cell-contents  undergo  a 
degeneration  which,  though  it  may  be  pathological,  is  very  often  a  normal 
process. 

Thus  we  have  (a.)  fatty  metamorphosis  producing  oil-globules  in  the 
secretion  of  milk,  fatty  degeneration  of  the  muscular  fibres  of  the  uterus 
after  the  birth  of  the  foetus,  and  of  the  cells  of  the  Graafian  follicle  giving 
rise  to  the  "corpus  luteum."  (See  chapter  on  Generation.) 

(b.)  Pigmentary  degeneration  from  deposit  of  pigment,  as  in  the  epi- 
thelium of  the  air-vesicles  of  the  lungs. 

(c.)  Calcareous  degeneration  which  is  common  in  the  cells  of  many 
cartilages. 

Having  thus  reviewed  the  life-history  of  cells  in  general,  we  may  now 
discuss  the  leading  varieties  of  form  which  they  present. 

In  passing,  it  may  be  well  to  point  out  the  main  distinctions  between 
animal  and  vegetable  cells. 


STRUCTURAL    BASIS    OF    THE    HUMAN    BODY. 


15 


It  has  been  already  mentioned  that  in  animal  cells  an  envelope  or  cell- 
wall  is  by  no  means  always  present.  In  adult  vegetable  cells,  on  the 
other  hand,  a  well-defined  cellulose  wall  is  highly  characteristic;  this,  it 
should  be  observed,  is  non-nitrogenous,  and  thus  differs  chemically  as 
well  as  structurally  from  the  contained  mass. 

Moreover,  in  vegetable  cells  (Fig.  8,  B),  the  protoplastic  contents  of 
tli3  cell  fall  into  two  subdivisions:  (1)  a  continuous  film  which  lines  the 
interior  of  the  cellulose  wall;  and  (2)  a  reticulate  mass  containing  the 


FIG.  8.— (A).  Young  vegetable  cells,  showing  cell-cavity  entirely  filled  with  granular  protoplasm 
enclosing  a  large  oval  nucleus,  with  one  or  more  nucleoli. 

(B.)  Older  cells  from  the  same  plant,  showing  distinct  cellulose- wall  and  vacuolation  of  proto- 
plasm. 

nucleus  and  occupying  the  cell-cavity;  its  interstices  are  filled  with  fluid. 
In  young  vegetable  cells  such  a  distinction  does  not  exist;  a  finely  gran- 
ular protoplasm  occupies  the  whole  cell-cavity  (Fig.  8,  A). 

Another  striking  difference  is  the  frequent  presence  of  a  large  quan- 
tity of  intercellular  substance  in  animal  tissues,  while  in  vegetables  it  is 
comparatively  rare,  the  requisite  consistency  being  given  to  their  tissues 
by  the  tough  cellulose  walls,  often  thickened  by  deposits  of  lignin.  In 
animal  cells  this  end  is  attained  by  the  deposition  of  lime-salts  in  a  matrix 
of  intercellular  substance,  as  in  the  process  of  ossification. 

Forms  of  Cells.— Starting  with  the  spherical  or  spheroidal  (Fig.  9,  a) 
as  the  typical  form  assumed  by  a  free  cell,  we  find  this  altered  to  a  poly- 
hedral shape  when  the  pressure  on  the  cells  in  all  directions  is  nearly  the 
same  (Fig.  9,  b). 

Of  this,  the  primitive  segmentation-cells  may  afford  an  example. 

The  discoid  shape  is  seen  in  blood-cells  (Fig.  9,  c),  and  the  scale-like 


FIG.  9.— Various  forms  of  cells,    a.  Spheroidal,  showing  nucleus  and  nucleolus.    6.  Polyhedral. 
c.  Discoidal  (blood-cells),    d.  Scaly  or  squamous  (epithelial  cells). 

form  in  superficial  epithelial  cells  (Fig.  9,  d).     Some  cells  have  a  jagged 
outline  (prickle-cells)  (Fig.  13). 

Cylindrical,  conical,  or  prismatic  cells  occur  in  the  deeper  layers  of 
laminated  epithelium,  and  the  simple  cylindrical  epithelium  of  the  intes- 
tino  and  many  gland  ducts.  Such  cells  may  taper  off  at  one  or  both 


16 


HAND-BOOK    OF    PHYSIOLOGY. 


ends  into  fine  processes,  in  the  former  case  being  caudate,  in  the  latter 
fusiform  (Fig.  10).  They  may  be  greatly  elongated  so  as  to  become 
fibres.  Ciliated  cells  (Fig.  10,  d)  must  be  noticed  as  a  distinct  variety: 
they  possess,  but  only  on  their  free  surfaces,  hair-like  processes  (cilia). 
These  vary  immensely  in  size,  and  may  even  exceed  in  length  the  cell 
itself.  Finally  we  have  the  branched  or  stellate  cells,  of  which  the  large 


\ 


FIG.  10.— Various  forms  of  cells,    a.  Cylindrical  or  columnar,    b.  Caudate,    c.  Fusiform,    d.  Cilia- 
ted (from  trachea),    e.  Branched,  stellate. 

nerve-cells  of  the  spinal  cord,  and  the  connective  tissue  corpuscle  are 
typical  examples  (Fig.  10,  e).  In  these  cells  the  primitive  branches  by 
secondary  branching  may  give  rise  to  an  intricate  network  of  processes. 

Classification  of  Cells. — Cells  may  be  classified  in  many  ways. 
According  to: — 

(a.)  Form  :  They  may  be  classified  into  spheroidal  or  polyhedral,  dis- 
coidal,  flat  or  scaly,  cylindrical,  caudate,  fusiform,  ciliated  and  stellate.. 

(b. )  Situation : — we  may  divide  them  into  blood  cells,  gland  cells, 
connective  tissue  cells,  etc. 

(c.)   Contents : — fat  and  pigment  cells  and  the  like. 

(d.)  Function: — secreting,  protective,  contractile,  etc. 

(e.)  Origin: — hypoblastic,  mesoblastic,  and  epiblastic  cells.  (See 
chapter  on  Generation.) 

It  remains  only  to  consider  the  various  ways  in  which  cells  are  con- 
nected together  to  form  tissues,  and  the  transformations  by  which  inter- 
cellular substance,  fibres  and  tubules  are  produced. 

Modes  of  connection. — Cells  are  connected: — 

(1)  By  a  cementing  intercellular  substance.  This  is  probably  always 
present  as  a  transparent,  colorless,  viscid,  albuminous  substance,  even 
between  the  closely  apposed  cells  of  cylindrical  epithelium,  while  in  the 
case  of  cartilage  it  forms  the  main  bulk  of  the  tissue,  and  the  cells  only 
appear  as  imbedded  in,  not  as  cemented  by,  the  intercellular  substance. 

This  intercellular  substance  may  be  either  homogeneous  or  fibrillated. 

In  many  cases  (e.g.  the  cornea)  it  can  be  shown  to  contain  a  number 


STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.  17 

of  irregular  branched  cavities,  which  communicate  with  each  other,  and 
in  wliich  the  branched  cells  lie:  through  these  branching  spaces  nutritive 
fluids  can  find  their  way  into  the  very  remotest  parts  of  a  non-vascular 
tissue. 

-  As  a  special  variety  of  intercellular  substance  must  be  mentioned  the 
basement  membrane  (membrana  propria)  which  is  found  at  the  base  of 
the  epithelial  cells  in  most  mucous  membranes,  and  especially  as  an  in- 
vesting tunic  of  gland  follicles  which  determines  their  shape,  and  which 
may  persist  as  a  hyaline  saccule  after  the  gland -cells  have  all  been  dis- 
charged. 

(2)  By  anastomosis  of  their  processes. 

This  is  the  usual  way  in  which  stellate  cells,  e.g.,  of  the  cornea,  are 
united:  the  individuality  of  each  cell  is  thus  to  a  great  extent  lost  by  its 
connection  with  its  neighbors  to  form  a  reticulum:  as  an  example  of  a  net- 
work so  produced,  we  may  cite  the  stroma  of  lymphatic  glands. 

Sometimes  the  branched  processes  breaking  up  into  a  maze  of  minute 
fibrils,  adjoining  cells  are  connected  by  an  intermediate  reticulum:  this 
is  the  case  in  the  n^rve-cells  of  the  spinal  cord. 

Besides  the  Cell,  which  may  be  termed  the  primary  tissue-element, 
there  are  materials  which  may  be  termed  secondary  or  derived  tissue- 
elements.  Such  are  Intercellular  substance,  Fibres  and  Tubules. 

Intercellular  substance  is  probably  in  all  cases  directly  derived  from 
the  cells  themselves.  In  some  cases  (e.g.  cartilage),  by  the  use  of  re- 
agents the  cementing  intercellular  substance  is,  as  it  were,  analyzed  into 
various  masses,  each  arranged  in  concentric  layers  around  a  cell  or  group 
of  cells,  from  which  it  was  probably  derived  (Fig.  6). 

Fibres. — In  the  case  of  the  crystalline  lens,  and  of  muscle  both  stri- 
ated and  non-striated,  each  fibre  is  simply  a  metamorphosed  cell:  in  the 
case  of  striped  fibre  the  elongation  being  accompanied  by  a  multiplication 
of  the  nuclei. 

The  various  fibres  and  fibrillae  of  connective  tissue  result  from  a  grad- 
ual transformation  of  an  originally  homogeneous  intercellular  substance. 
Fibres  thus  formed  may  undergo  great  chemical  as  well  as  physical  trans- 
formation: this  is  notably  the  case  with  yellow  elastic  tissue,  in  which 
the  sharply  defined  elastic  fibres,  possessing  great  power  of  resistance  to 
re-agents,  contrast  strikingly  with  the  homogeneous  matter  from  which 
they  are  derived. 

Tubules  which  were  originally  supposed  to  consist  of  structureless 
membrane,  have  now  been  proved  to  be  composed  of  flat,  thin  cells, 
cohering  along  their  edges.  (See  Capillaries.) 

With  these  simple  materials  the  various  parts  of  the  body  are  built  up; 
the  more  elementary  tissues  being,   so   to  speak,   first  compounded  of 
VOL.  I.— 2. 


18  HAND-BOOK    OF    PHYSIOLOGY. 

them;    while  these  again  are  variously  mixed  and  interwoven  to  form 
more  intricate  combinations. 

Thus  are  constructed  epithelium  and  its  modifications,  connective 
tissue,  fat,  cartilage,  bone,  the  fibres  of  muscle  and  nerve,  etc. ;  and  these, 
again,  with  the  more  simple  structures  before  mentioned,  are  used  as 
materials  wherewith  to  form  arteries,  veins,  and  lymphatics,  secreting 
and  vascular  glands,  lungs,  heart,  liver,  and  other  parts  of  the  body. 


CHAPTER  III. 

STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 

IN  this  chapter  the  leading  characters  and  chief  modifications  of  two 
great  groups  of  tissues — the  Epithelial  and  Connective — will  be  briefly  de- 
scribed; while  the  Nervous  and  Muscular,  together  with  several  other 
more  highly  specialized  tissues,  will  be  appropriately  considered  in  the 
chapters  treating  of  their  physiology. 

EPITHELIUM. 

* 

Epithelium  is  composed  of  cells  of  various  shapes  held  together  by  a 
small  quantity  of  cementing  intercellular  substance. 

Epithelium  clothes  the  whole  exterior  surface  of  the  body,  forming 
the  epidermis  with  its  appendages — nails  and  hairs;  becoming  continuous 
at  the  chief  orifices  of  the  body — nose,  mouth,  anus,  and  urethra — with 
the  epithelium  which  lines  the  whole  length  of  the  alimentary  and  genito- 
urinary tracts,  together  with  the  ducts  of  their  various  glands.  Epi- 
thelium also  lines  the  cavities  of  the  brain,  and  the  central  canal  of  the 
spinal  cord,  the  serous  and  synovial  membranes,  and  the  interior  of  all 
blood-vessels  and  lymphatics. 

The  cells  composing  it  may  be  arranged  in  either  one  or  more  layers, 
and  thus  it  may  be  subdivided  into  (a)  Simple  and  (b)  Stratified  or 
laminated  Epithelium.  A  simple  epithelium,  for  example,  lines  the 
whole  intestinal  mucous  membrane  from  the  stomach  to  the  anus:  the 
epidermis  on  the  other  hand  is  laminated  throughout  its  entire  extent. 

Epithelial  cells  possess  an  intracellular  and  an  intranuclear  network 
(p.  10).  They  are  held  together  by  a  clear,  albuminous,  cement  sub- 
stance. The  viscid  semi-fluid  consistency  both  of  cells  and  intercellular 
substance  permits  such  changes  of  shape  and  arrangement  in  the  individ- 
ual cells  as  are  necessary  if  the  epithelium  is  to  maintain  its  integrity  in 
organs  the  area  of  whose  free  surface  is  so  constantly  changing,  as  the 
stomach,  lungs,  etc.  Thus,  if  there  be  but  a  single  layer  of  cells,  as  in 
the  epithelium  lining  the  air  vesicles  of  the  lungs,  the  stretching  of  this 
membrane  causes  such  a  thinning  out  of  the  cells  that  they  change  their 
shape  from  spheroidal  or  short  columnar,  to  squamous,  and  vice  versa, 
when  the  membrane  shrinks. 


20 


HAND-BOOK    OF    PHYSIOLOGY. 


CLASSIFICATION  OF  EPITHELIAL  CELLS. 

Epithelial  cells  may  be  conveniently  classified  as: 

1.  Sguamous,  scaly,  pavement,  or  tessellated. 

2.  Spheroidal,  glandular,  or  polyhedral 

3.  Columnar,  cylindrical)  conical,  or  goblet-shaped. 

4.  Ciliated. 

5.  Transitional. 

Although,  for  convenience,  epithelial  cells  are  thus  classified,  yet  the 
first  three  forms  of  cells  are  sometimes  met  with  at  different  depths  in 


FIG.  11.— Vertical  section  of  Rabbit's  cornea,  a.  Anterior  epithelium,  showing  the  different 
shapes  of  the  cells  at  various  depths  from  the  free  surface,  b.  Portion  of  the  substance  of  cornea. 
(Klein.) 

the  same  membrane.  As  an  example  of  such  a  laminated  epithelium 
showing  these  different  cell-forms  at  various  depths,  we  may  select  the 
anterior  epithelium  of  the  cornea  (Fig.  11). 

1.  Sguamous  Epithelium  (Fig.  12). — Arranged.  (A)  in  several  super- 
posed layers  (stratified  or  laminated),  this  form  of  epithelium  covers  (a) 
the  skin,  where  it  is  called  the  Epidermis,  and  lines  (b)  the  mouth, 

pharynx,  and  oesophagus,  (c)  the  conjunc- 
tiva, (d)  the  vagina,  and  entrance  of  the 
urethra  in  both  sexes;  while,  as  (B)  a  single 
layer,  the  same  kind  of  epithelium  forms 
(a)  the  pigmentary  layer  of  the  retina, 
and  lines  (b)  the  interior  of  the  serous  and 
synoviul  sacs,  and  (c)  of  the  heart,  blood 
and  lymph- vessels  (Endothelium).  It  con- 
sists of  cells,  which  are  flattened  and  scaly, 
with  an  irregular  outline:  and,  when  laminated,  may  form  a  dense  horny 
investment,  as  on  parts  of  the  palms  of  the  hands  and  soles  of  the  feet. 
The  nucleus  is  often  not  apparent.  The  really  cellular  nature  of  even 
the  dry  and  shriveled  scales  cast  off  from  the  surface  of  the  epidermis, 
can  be  proved  by  the  application  of  caustic  potash,  which  causes  them 
rapidly  to  swell  and  assume  their  original  form. 


FIG.  12.— Squamous  epithelium  scales 
from  the  inside  of  the  mouth.  X  260. 
(Henle.) 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  21 

Squamous  cells  are  generally  united  by  an  intercellular  substance;  but 
in  many  of  the  deeper  layers  of  epithelium  in  the  mouth  and  skin,  the 
outline  of  the  cells  is  very  irregular. 

Such  cells  (Fig.  13)  are  termed  "ridge  and  furrow/'  "cogged"  or 
"prickle"  cells.  These  "prickles"  are  prolongations  of  the  intra-cellular 
network  which  run  across  from  cell  to  cell,  thus  joining  them  together, 
the  interstices  being  filled  by  the  transparent  intercellular  cement  sub- 
stance. When  this  increases  in  quantity  in  inflammation,  the  cells  are 
pushed  further  apart  and  the  connecting  fibrils  or  "prickles"  elongated, 
and  therefore  more  clearly  visible. 

Squamous  epithelium,  e.g.  the  pigment  cells  of  the  retina,  may  have 
a  deposit  of  pigment  in  the  cell-substance.  This  pigment  consists  of 
minute  molecules  of  melanin,  imbedded  in  the  cell-substance  and  almost 
concealing  the  nucleus,  which  is  itself  transparent  (Fig.  14). 

In  white  rabbits  and  other  albino  animals,  in  which  the  pigment  of 


FIG.  13.  FIG.  14. 

FIG.  13.— Jagged  cells  of  the  middle  layers  of  pavement  epithelium,  from  a  vertical  section  of 
the  gum  of  a  new-born  infant.  (Klein.) 

FIG.  14.— Pigment  cells  from  the  retina.  A,  cells  still  cohering,  seen  on  their  surface;  a,  nucleus 
indistinctly  seen.  In  the  other  cells  the  nucleus  is  concealed  by  the  pigment  granules.  B,  two  cells 
seen  in  profile;  a,  the  outer  or  posterior  part  containing  scarcely  any  pigment,  x  370.  (Henle.) 

the  eye  is  absent,  this  layer  is  found  to  consist  of  colorless  pavement 
epithelial  cells. 

Endothelium. — The  squamous  epithelium  lining  the  serous  mem- 
branes, and  the  interior  of  blood-vessels,  presents  so  many  special  features 
as  to  demand  a  special  description;  it  is  called  by  a  distinct  name — En- 
dothelium. 

The  main  points  of  distinction  above  alluded  to  are,  1.  the  very  flat- 
tened form  of  these  cells;  2.  their  constant  occurrence  in  only  a  single 
layer;  3.  the  fact  that  they  are  developed  from  the  "mesoblast,"  while 
all  other  epithelial  cells  are  derived  from  the  "epiblast,"  or  "hypoblast;" 
4.  they  line  closed  cavities  not  communicating  with  the  exterior  of  the 
body.  Endothelial  cells  form  an  important  and  well-defined  subdivision 
of  squamous  epithelial  cells,  which  has  been  especially  studied  during 
the  last  few  years.  Their  examination  has  been  much  facilitated  by  the 
adoption  of  the  method  of  staining  serous  membranes  with  silver  nitrate. 


22 


HAND-BOOK    OF    PHYSIOLOGY. 


When  a  small  portion  of  a  perfectly  fresh  serous  membrane,  as  the 
mesentery  or  omentum  (Fig.  15),  is  immersed  for  a  few  minutes  in  a 
quarter  per  cent,  solution  of  this  re-agent,  washed  with  water  and  exposed 
to  the  action  of  light,  the  silver  oxide  is  precipitated  along  the  bounda- 


Fio.  15.— Part  of  the  omentum  of  a  cat,  stained  in  silver  nitrate,  X  100.  The  tissue  forms  a  "fenes- 
trated  membrane,"  that  is  to  say,  one  which  is  studded  with  holes  or  windows.  In  the  figure  these 
are  of  various  shapes  and  sizes,  leaving  trabeculae,  the  basis  of  which  is  fibrous  tissue.  The  trabecu- 
Ise  are  of  various  sizes,  and  are  covered  with  endothelial  cells,  the  nuclei  of  which  have  been  made 
evident  by  staining  with  hasmatoxylin  after  the  silver  nitrate  has  outlined  the  cells  by  staining  the 
intercellular  substance.  (V.  D.  Harris.) 

ries  of  the  cells,  and  the  whole  surface  is  found  to  be  marked  out  with 
exquisite  delicacy,  by  fine  dark  lines,  into  a  number  of  polygonal  spaces 
(endothelial  cells)  (Figs.  15  and  16). 

Endothelium  lines,  as  before  mentioned,  all  the  serous  cavities  of  the 


FIG.  16.— Abdominal  surface  of  centrum  tendineum  of  diaphragm  of  rabbit,  showing  the  general 
polygonal  shape  of  the  endothelial  cells;  each  is  nucleated.    (Klein.)    x  300. 

body,  including  the  anterior  chamber  of  the  eye,  also  the  synovial  mem- 
branes of  joints,  and  the  interior  of  the  heart  and  of  all  blood-vessels  and 
lymphatics.  It  forms  also  a  delicate  investing  sheath  for  nerve-fibres 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  23 

and  peripheral  ganglion-cells.  The  cells  are  scaly  in  form,  and  irregular 
in  outline;  those  lining  the  interior  of  blood-vessels  and  lymphatics  hav- 
ing a  spindle-shape  with  a  very  wavy  outline.  They  enclose  a  clear,  oval 
nucleus,  which,  when  the  cell  is  viewed  in  profile,  is  seen  to  project  from 
its  surface. 

Endothelial  cells  may  be  ciliated,  e.g.,  those  in  the  mesentery  of 
frogs,  especially  about  the  breeding  season. 

Besides  the  ordinary  endothelial  cells  above  described,  there  are  found 
on  the  omentum  and  parts  of  the  pleura  of  many  animals,  little  bud-like 
processes  or  nodules,  consisting  of  small  polyhedral  granular  cells,  round- 
ed on  their  free  surface,  which  multiply  very  rapidly  by  division  (Fig. 
17).  These  constitute  what  is  known  as  "germinating  endothelium." 


FIG.  1  i .— Suver-stained  preparation  of  great  omentum  of  dog,  which  shows,  amongst  the  flat 
endothehum  of  the  surface,  small  and  large  groups  of  germinating  endothelium,  between  which 
numbers  of  stomata  are  to  be  seen.  (Klein.)  x  300. 

The  process  of  germination  doubtless  goes  on  in  health,  and  the  small  cells 
which  are  thrown  off  in  succession  are  carried  into  the  lymphatics,  and 
contribute  to  the  number  of  the  lymph  corpuscles.  The  buds  may  be 
enormously  increased  both  in  number  and  size  in  certain  diseased  condi- 
tions. 

On  those  portions  of  the  peritoneum  and  other  serous  membranes 
where  lymphatics  abound,  there  are  numerous  small  orifices — stomata — 
(Fig.  18)  between  the  endothelial  cells:  these  are  really  the  open  mouths 
of  lymphatic  vessels,  and  through  them  lymph -corpuscles,  and  the  serous 
fluid  from  the  serous  cavity,  pass  into  the  lymphatic  system. 

2.  Split  roiihil  epithelial  cells  are  the  active  secreting  agents  in  most 


24 


HAND-BOOK    OF    PHYSIOLOGY. 


secreting  glands,  and  hence  are  often  termed  glandular;  they  are  gener- 
ally more  or  less  rounded  in  outline:  often  polygonal  from  mutual  pres- 
sure. 


FIG.  18.— Peritoneal  surface  of  septum  cisternse  lymphaticae  magnae  of  frog.  The  stomata,  some 
of  which  are  open;  some  collapsed,  are  surrounded  by  germinating  endothelium.  (Klein.)  x  160. 

Excellent  examples  are  to  be  found  in  the  liver,  the  secreting  tubes  of 
the  kidney,  and  in  the  salivary  and  peptic  glands  (Fig.  19). 

3.  Columnar  epithelium  (Fig.  20,  A  and  B)  lines  (a.)  the  mucous  mem- 
brane of  the  stomach  and  intestines,  from  the  cardiac  orifice  of  the  stomach 
to  the  anus,  and  (b. )  wholly  or  in  part  the  ducts  of  the  glands  opening  on 


FIG.  19.— Glandular  epithelium.    A,  small  lobule  of  a  mucous  gland  of  the  tongue,  showing  nu- 
cleated glandular  spheroidal  cells.    B,  Liver  cells.     X  200.    (V.  D.  Harris.) 

its  free  surface;  also  (c.)  many  gland-ducts  in  other  regions  of  the  body, 
e.g.,  mammary,  salivary,  etc.;  (d.)  the  cells  which  form  the  deeper  layers 
of  the  epithelial  lining  of  the  trachea  are  approximately  columnar. 

It  consists  of  cells  which  are  cylindrical  or  prismatic  in  form,  and  con- 
tain a  large  oval  nucleus.  When  evenly  packed  side  by  side  as  a  single 
layer,  the  cells  are  uniformly  columnar;  but  when  occurring  in  several 
layers  as  in  the  deeper  strata  of  the  epithelial  lining  of  the  trachea,  their 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


25 


shape  is  very  variable,  and  often  departs  very  widely  from  the  typical 
columnar  form. 

(Inhli't-a'U*. — Many  cylindrical  epithelial  cells  undergo  a  curious  trans- 
formation, and  from  the  alteration  in  their  shape  are  termed  goblet-cells 
(Fi«r.  V<».  A,  c,  andB). 

These  are  never  seen  in  a  perfectly  fresh  specimen:  but  if  such  a 
specimen  be  watched  for  some  time,  little  knobs  are  seen  gradually  appear- 


FIG.  20.— A.  Vertical  section  of  a  villus  of  the  small  intestine  of  a  cat.  a.  Striated  basilar  border 
of  the  epithelium,  b.  Columnar  epithelium,  c.  Goblet  cells,  d.  Central  lymph-vessel,  e.  Smooth 
muscular  fibres.  /.  Adenoid  stroma  of  the  villus  in  which  lymph  corpuscles  lie.  B.  Goblet  cells. 
(Klein.) 

ing  on  the  free  surface  of  the  epithelium,  and  are  finally  detached;  these 
consist  of  the  cell-cont3nts  which  are  discharged  by  the  open  mouth  of 
the  goblet,  leaving  the  nucleus  surrounded  by  the  remains  of  the  proto- 
plasm in  its  narrow  stem. 

Some  regard  this  transformation  as  a  normal  process  which  is  continu- 
ally going  on  during  life,  the  discharged  cell-contents  contributing  to  form 
mucus,  the  cells  being  supposed  in  many  cases  to  recover  their  original 
shape. 

The  columnar  epithelial  cells  of  the  alimentary  canal  possess  a  struc- 
tureless layer  on  their  free  surface:  such  a  layer,  appearing  striated  when 
viewed  in  section,  is  termed  the  "striated  basilar  border"  (Fig.  20,  A,  a). 

4.  Ciliated  cells  are  generally  cylindrical  (Fig.  21,  B),  but  may  be 
spheroidal  or  even  almost  squamous  in  shape  (Fig.  21,  A). 

This  form  of  epithelium  lines  (a.)  the  whole  of  the  respiratory  tract 
from  the  larynx  to  the  finest  subdivisions  of  the  bronchi,  also  the  lower 
parts  of  the  nasal  passages,  and  some  portions  of  the  generative  apparatus 
— in  the  male  (b.)  lining  the  "vasa  efferentia"  of  the  testicle,  and  .their 
prolongations  as  far  as  the  lower  end  of  the  epididymis;  in  the  female 
(c. )  commencing  about  the  middle  of  the  neck  of  the  uterus,  and  extend- 
ing throughout  the  uterus  and  Fallopian  tubes  to  their  fimbriated  ex- 
tremities, and  even  for  a  short  distance  on  the  peritoneal  surface  of  the 
latter,  (d.)  The  ventricles  of  the  brain  and  the  central  canal  of  the 


26  HAND-BOOK    OF    PHYSIOLOGY. 

spinal  cord  are  clothed  with  ciliated  epithelium  in  the  child,  but  in  the 
adult  it  is  limited  to  the  central  canal  of  the  cord. 

The  Cilia,  or  fine  hair-like  processes  which  give  the  name  to  this  va- 
riety of  epithelium,  vary  a  good  deal  in  size  in  different  classes  of  animals, 
being  very  much  smaller  in  the  higher  than  among  the  lower  orders,  in 
which  they  sometimes  exceed  in  length  the  cell  itself. 

The  number  of  cilia  on  any  one  cell  ranges  from  ten  to  thirty,  and 
those  attached  to  the  same  cell  are  often  of  different  lengths.  When  liv- 
ing ciliated  epithelium,  e.g..,  the  gill  of  a  mussel,  is  examined  under  the 
microscope,  the  cilia  are  seen  to  be  in  constant  rapid  motion;  each  cilium 
being  fixed  at  one  end,  and  swinging  or  lashing  to  and  fro.  The  gen- 
eral impression  given  to  the  eye  of  the  observer  is  very  similar  to  that  pro- 
duced by  waves  in  a  field  of  corn,  or  swiftly  running  and  rippling  water, 


FIG.  21.— A.  Spheroidal  ciliated  cells  from  the  mouth  of  the  frog.     X  300  diameters.    (Sharpey.) 
B.  a.  Ciliated  columnar  epithelium  lining  a  bronchus,     b.  Branched  connective-tissue  corpuscles. 

(Klein  and  Noble  Smith.) 

and  the  result  of  their  movement  is  to  produce  a  continuous  current  in 
a  definite  direction,  and  this  direction  is  invariably  the  same  on  the  same 
surface,  being  always,  in  the  case  of  a  cavity,  toward  its  external  orifice. 

5.  Transitional  Epithelium-. — This  term  has  been  applied  to  cells 
which  are  neither  arranged  in  a  single  layer,  as  is  the  case  with  simple 
epithelium,  nor  yet  in  many  superimposed  strata  as  in  laminated;  in  other 
words,  the  term  is  employed  when  epithelial  cells  are  found  in  two,  three, 
or  four  superimposed  layers.  The  upper  layer  may  be  either  columnar, 
ciliated,  or  squamous.  When  the  upper  layer  is  columnar  or  ciliated,  the 
second  layer  consists  of  smaller  cells  fitted  into  the  inequalities  of  the 
cells  above  them,  as  in  the  trachea  (Fig.  21,  B).  The  epithelium  which 
is  met  with  lining  the  urinary  bladder  and  ureters  is,  however,  the  tran- 
sitional par  excellence.  In  this  variety  there  are  two  or  three  layers  of 
cells,  the  upper  being  more  or  less  flattened  according  to  the  full  or  col- 
lapsed condition  of  the  organ,  their  under  surface  being  marked  with 
one  or  more  depressions,  into  which  the  heads  of  the  next  layer  of  club- 
shaped  cells  fit.  Between  the  lower  and  narrower  parts  of  the  second  row 
of  cells,  are  fixed  the  irregular  cells  which  constitute  the  third  row,  and 
in  like  manner  sometimes  a  fourth  row  (Fig.  22).  It  can  be  easily  under- 
stood, therefore,  that  if  a  scraping  of  the  mucous  membrane  of  the  blad- 


STKl(  TIKE    OF    THE    ELEMENTARY    TISSUES.  27 

der  be  teazed,  and  examined  under  the  microscope,  cells  of  a  great  variety 
of  forms  may  be  made  out  (Fig.  23).  Each  cell  contains  a  large  nucleus, 
and  the  larger  and  superficial  cells  often  possess  two. 

Special  Epithelium  in  Organs  of  Special  Sense.— In  addition 
to -the  above  kinds  of  epithelium,  certain  highly  specialized  forms  of  epi- 
thelial cells  are  found  in  the  organs  of  smell,  sight, 'and  hearing,  viz., 


FIG.  22.  FIG.  23. 

FIG.  22.— Epithelium  of  the  bladder;  a,  one  of  the  cells  of  the  first  row;  6,  a  cell  of  the  second 
row:  c,  cells  in  situ,  of  first,  second,  and  deepest  layers.  (Obersteiner.) 

FIG.  23. — Transitional  epithelial  cells  from  a  scraping  of  the  mucous  membrane  of  the  bladder  of 
the  rabbit.  (V.  D.  Harris.) 

olfactory  cells,   retinal  rods  and  cones,  auditory  cells;  they  will  be  de- 
scribed in  the  chapters  which  deal  with  their  functions. 

Functions  of  Epithelium. — According  to  function,  epithelial  cells 
may  be  classified  as: — 

(1.)  Protective,  e.g.,  in  the  skin,  mouth,  blood-vessels,  etc. 

(2.)  Protective  and  moving — ciliated  epithelium. 

(3.)  Secreting — glandular  epithelium;  or,  Secreting  formed  elements 
— epithelium  of  testicle  secreting  spermatozoa. 

(4.)  Protective  and  secreting,  e.g.,  epithelium  of  intestine. 

(5.)  Sensorial,  e.g.,  olfactory  cells,  rods  and  cones  of  retina,  organ  of 
Corti. 

Epithelium  forms  a  continuous  smooth  investment  over  the  whole 
body,  being  thickened  into  a  hard,  horny  tissue  at  the  points  most  ex- 
posed to  pressure,  and  developing  various  appendages,  such  as  hairs  and 
nails,  whose  structure  and  functions  will  be  considered  in  a  future  chapter. 
Epithelium  lines  also  the  sensorial  surfaces  of  the  eye,  ear,  nose,  and 
mouth,  and  thus  serves  as  the  medium  through  which  all  impressions 
from  the  external  world — touch,  smell,  taste,  sight,  hearing — reach  the 
delicate  nerve-endings,  whence  they  are  conveyed  to  the  brain. 

The  ciliated  epithelium  which  lines  the  air-passages  serves  not  only 
as  a  protective  investment,  but  also  by  the  movements  of  its  cilia  is  en- 
abled to  propel  fluids  and  minute  particles  of  solid  matter  so  as  to  aid 
their  expulsion  from  the  body.  In  the  case  of  the  Fallopian  tube,  this 


28  HAND-BOOK    OF    PHYSIOLOGY. 

agency  assists  the  progress  of  the  ovum  toward  the  cavity  of  the  uterus. 
Of  the  purposes  served  by  cilia  in  the  ventricles  of  the  brain,  nothing  is 
known.  (For  an  account  of  the  nature  and  conditions  of  ciliary  motion, 
see  chapter  on  Motion.) 

The  epithelium  of  the  various  glands,  and  of  the  whole  intestinal 
tract,  has  the  power  of  secretion,  i.e.,  of  chemically  transforming  certain 
materials  of  the  blood;  in  the  case  of  mucus  and  saliva  this  has  been 
proved  to  involve  the  transformation  of  the  epithelial  cells  themselves; 
the  cell-substance  of  the  epithelial  cells  of  the  intestine  being  discharged 
by  the  rupture  of  their  envelopes,  as  mucus. 

Epithelium  is  likewise  concerned  in  the  processes  of  transudation,  dif- 
fusion, and  absorption. 

It  is  constantly  being  shed  at  the  free  surface,  and  reproduced  in  the 
deeper  layers.  The  various  stages  of  its  growth  and  development  can  be 
well  seen  in  a  section  of  any  laminated  epithelium,  such  as  the  epidermis. 

THE  CONNECTIVE  TISSUES. 

This  group  of  tissues  forms  the  Skeleton  with  its  various  connections 
— bones,  cartilages,  and  ligaments — and  also  affords  a  supporting  frame- 
work and  investment  to  various  organs  composed  of  nervous,  muscular, 
and  glandular  tissue.  Its  chief  function  is  the  mechancial  one  of  sup- 
port, and  for  this  purpose  it  is  so  intimately  interwoven  with  nearly  all 
the  textures  of  the  body,  that  if  all  other  tissues  could  be  removed,  and 
the  connective  tissues  left,  we  should  have  a  wonderfully  exact  model  of 
almost  every  organ  and  tissue  in  the  body,  correct  even  to  the  smallest 
minutiae  of  structure. 

Classification  of  Connective  Tissues. — The  chief  varieties  of 
connective  tissues  may  be  thus  classified: — 

I.  THE  FIBROUS  CONNECTIVE  TISSUES. 

A. — Chief  Forms.  -B. — Special  Varieties, 

a.  Areolar.  a.  Gelatinous. 

~b.  White  fibrous.  ~b.  Adenoid  or  Retiform. 

c.  Elastic.  c.  Neuroglia. 

d.  Adipose. 

II.  CARTILAGE. 
III.  BONE. 

All  of  the  varieties  of  connective  tissue  are  made  up  of  two  parts, 
namely,  cells  and  intercellular  substance. 
Cells. — The  cells  are  of  two  kinds. 
(a.)  Fixed. — These  are  cells  of  a  flattened  shape,  with  branched  pro- 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


-•'8,  which  are  often  united  together  to  form  a  network:  they  can  be 
most  readily  observed  in  the  cornea  in  which  they  are  arranged,  layer 
above  layer,  parallel  to  the  free  surface.  They  lie  in  spaces,  in  the  inter- 
cellular or  ground  substance,  which  are  of  the  same  shape  as  the  cells 
tlu-v  contain  but  rather  larger,  and  which  form  by  anastomosis  a  system 
of  branching  canals  freely  communicating  (Fig.  2-4). 


Fig.  24.— Horizontal  preparation  of  cornea  of  frog,  stained  in  gold  chloride;  showing  the  network 
of  branched  cornea  corpuscles.    The  ground-substance  is  completely  colorless.     X  400.    (Klein.) 

To  this  class  of  cells  belong  the  flattened  tendon  corpuscles  which  are 
arranged  in  long  lines  or  rows  parallel  to  the  fibres  (Fig.  29). 

These  branched  cells,  in  certain  situations,  contain  a  number  of  pig- 
ment-granules, giving  them  a  dark  appearance:  they  form  one  variety  of 
pigment-cells.  Branched  pigment-cells  of  this  kind  are  found  in  the 
outer  layers  of  the  choroid  (Fig.  25).  In  many 
lower  animals,  such  as  the  frog,  they  are  found 
widely  distributed,  not  only  in  the  skin,  but  also  in 
many  internal  parts,  e.g.,  the  mesentery  and  sheaths 
of  blood-vessels.  In  the  web  of  the  frog's  foot  such 
pigment-cells  may  be  seen,  with  pigment  evenly 
distributed  through  the  body  of  the  cell  and  its 
processes;  but  under  the  action  of  light,  electricity, 
and  other  stimuli,  the  pigment-granules  become 
massed  in  the  body  of  the  cell,  leaving  the  processes 
quite  hyaline;  if  the  stimulus  be  removed,  they 
will  gradually  be  distributed  again  all  over  the  pro- 
cesses. Thus  the  skin  in  the  frog  is  sometimes 


FIG.  25.— Ramified  pig- 
ment-cells from  the  tissue 
of  the  choroid  coat  of  the 
eye.  X  350.  a,  cell  with 
pigment;  6,  colorless 
form  cells.  (Kolliker.) 

In  the  choroid  and  retina  the  pigment- 


*y  - 

pigment;   6,  colorless  fusi- 

uniformly  dusky,  and   sometimes  quite  light-col- 
ored, with  isolated  dark  spots, 
cells  absorb  light. 

(b.)  Amoeboid  cells,  of  an  approximately  spherical  shape:  they  have  a 
great  general  resemblance  to  colorless   blood   corpuscles  (Fig.  2),  with 


30  HAND-BOOK    OF    PHYSIOLOGY. 

which  some  of  them  are  probably  identical.  They  consist  of  finely  gran- 
ular nucleated  protoplasm,  and  have  the  property,  not  only  of  changing 
their  form,  but  also  of  moving  about,  whence  they  are  termed  migra- 
tory. They  are  readily  distinguished  from  the  branched  connective-tissue 
corpuscles  by  their  free  condition,  and  the  absence  of  processes.  Some 
are  much  larger  than  others,  and  are  found  especially  in  the  sublingual 
gland  of  the  dog  and  guinea  pig  and  in  the  mucous  membrane  of  the 
intestine.  A  second  variety  of  these  cells  called  plasma  cells  (Waldeyer) 
are  larger  than  the  amoeboid  cells,  apparently  granular,  less  active  in  their 
movements.  They  are  chiefly  to  be  found  in  the  inter-muscular  septa, 
in  the  mucous  and  submucous  coats  of  the  intestine,  in  lymphatic  glands, 
and  in  the  omentum. 

Intercellular  Substance. — This  may  be  fibrillar,  as  in  the  fibrous 
tissues  and  certain  varieties  of  cartilage;  or  homogeneous,  as  in  hyaline 
cartilage. 


FIG.  26.  FIG.  27. 

FIG.  26.— Flat,  pigmented,  branched,  connective-tissue  cells  from  the  sheath  of  a  large  blood-ves- 
sel of  frog's  mesentery:  the  pigment  is  not  distributed  uniformly  through  the  substance  of  the  larger* 
cell,  consequently  some  parts  of  the  cell  look  blacker  than  others  (uncontracted  state).  In  the  two 
smaller  cells  most  of  the  pigment  is  withdrawn  into  the  cell-body,  so  that  they  appear  smaller,  black- 
er, and  less  branched,  x  350.  (Klein  and  Noble  Smith.) 

FIG.  27.— Fibrous  tissue  of  cornea,  showing  bundles  of  fibres  with  a  few  scattered  fusiform  cells 
lying  in  the  inter-fascicular  spaces.  X  400.  (Klein  and  Noble  Smith.) 

The  fibres  composing  the  former-are  of  two  kinds — (a.)  White  fibres. 
(b.)  Yellow  elastic  fibres. 

(a.)  White  Fibres. — These  are  arranged  parallel  to  each  other  in  wavy 
bundles  of  various  sizes:  such  bundles  may  either  have  a  parallel  arrange- 
ment (Fig.  27),  or  may  produce  quite  a  felted  texture  by  their  interlace- 
ment. The  individual  fibres  composing  these  fasciculi  are  homogeneous, 
unbranched,  and  of  the  same  diameter  throughout.  They  can  readily 
be  isolated  by  macerating  a  portion  of  white  fibrous  tissue  (e.g.,  a  small 
piece  of  tendon)  for  a  short  time  in  lime,  or  baryta-water,  or  in  a  solution 
of  common  salt,  or  potassium  permanganate:  these  reagents  possessing 
the  power  of  dissolving  the  cementing  interfibrillar  substance  (which  is 
nearly  allied  to  syntonin),  and  thus  separating  the  fibres  from  each  other. 

(b.)  Yelloiu  Elastic  Fibres  (Fig.  28)  are  of  all  sizes,  from  excessively 
fine  fibrils  up  to  fibres  of  considerable  thickness:  they  are  distinguished 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


31 


Fro.  28.— Elastic  fibres  from  the 
ligamentasubflava.    x  200.  (Shar- 


from  white  fibres  by  the  following  characters: — (1.)  Their  great  power  of 
resistance  even  to  the  prolonged  action  of  chemical  reagents,  e.g.,  Caustic 
Soda,  Acetic  Acid,  etc.  (2.)  Their  well-de- 
iined  outlines/  (3.)  Their  great  tendency  to 
branch  and  form  networks  by  anastomosis.  (4. ) 
They  very  often  have  a  twisted  corkscrew- 
like  appearance,  and  their  free  ends  usually 
curl  up.  (5.)  They  are  of  a  yellowish  tint 
and  very  elastic. 

VARIETIES   OF   CONNECTIVE   TISSUE. 
I.  FIBROUS  CONNECTIVE  TISSUES. 

A. — Chief  Forms. — (a.)  Areolar  Tissue. 

Distribution. — This  variety  has  a  very  wide 
distribution,  and  constitutes  the  subcutaneous, 
subserous  and  submucous  tissue.     It  is  found 
in  the  mucous  membranes,  in  the  true  skin,  in     pej-) 
the  outer  sheaths  of   the  blood-vessels.     It  forms  sheaths  for  muscles, 
nerves,  glands,  and  the  internal  organs,  and,  penetrating  into  their  in- 
terior, supports  and  connects  the  finest  parts. 

Structure. — To  the  naked  eye  it  appears,  when  stretched  out,  as  a 
fleecy,  white,  and  soft  meshwork  of  fine  fibrils,  with  here  and  there  wider 
films  joining  in  it,  the  whole  tissue  being  evidently  elastic.  The  open- 
ness of  the  meshwork  varies  with  the  locality  from  which  the  specimen  is 
taken.  On  the  addition  of  acetic  acid  the  tissue  swells  up,  and  becomes 
gelatinous  in  appearance.  Under  the  microscope  it  is  found  to  be  made 
up  of  fine  white  fibres,  which  interlace  in  a  most  irregular  manner,  to- 
gether with  a  variable  number  of  elastic  fibres.  These  latter  resist  the 
action  of  acetic  acid  as  above  mentioned,  so  that  when  this  reagent  is 
added  to  a  specimen  of  areolar  tissue,  although  the  white  fibres  swell  up 
and  become  homogeneous,  certain  elastic  fibres  may  still  be  seen  arranged 
in  various  directions,  sometimes  even  appearing  to  pass  in  a  more  or  less 
circular  or  in  a  spiral  manner  round  a  small  mass  of  the  gelatinous  mass 
of  changed  white  fibres.  The  cells  of  the  tissue  are  arranged  in  no  very 
regular  manner,  being  contained  in  the  spaces  (areolse)  between  the  fibres. 
They  communicate,  however,  with  one  another  by  their  branched  pro- 
cesses, and  also  apparently  with  the  cells  forming  the  walls  of  the  capil- 
lary blood-vessels  in  their  neighborhood,  connecting  together  the  fibrils 
in  a  certain  amount  of  albuminous  cement  substance. 

(b.)    White  Fibrous  Tissue. 

Distribution. — Typically  in  tendon;  in  ligaments,  in  the  periosteum 
and  perichondrium,  the  dura  mater,  the  pericardium,  the  sclerotic  coat 


32 


HAND-BOOK    OF    PHYSIOLOGY. 


of  the  eye,  the  fibrous  sheath  of  the  testicle;  in  the  fasciae  and  aponeurosis 
of  muscles,  and  in  the  sheaths  of  lymphatic  glands. 

Structure. — To  the  naked  eye/ tendons  and  many  of  the  fibrous  mem- 
branes, when  in  a  fresh  state,  present  an  appearance  as  of  watered  silk. 
This  is  due  to  the  arrangement  of  the  fibres  in  wavy  parallel  bundles. 
Under  the  microscope,  the  tissue  appears  to  consist  of  long,  often  parallel, 
wavy  bundles  of  fibres  of  different  sizes.  Sometimes  the  fibres  intersect 
each  other.  The  cells  in  tendons  are  arranged  in  long  chains  in  the 
ground  substance  separating  the  bundles  of  fibres,  and  are  more  or  less 
regularly  quadrilateral  with  large  round  nuclei  containing  nucleoli,  which 
are  generally  placed  so  as  to  be  contiguous  in  two  cells.  The  cells  consist 
of  a  body,  which  is  thick,  from  which  processes  pass  in  various  directions 
into,  and  partially  filling  up  the  spaces  between  the  bundles  of  fibres. 


FIG.  29. 


FIG.  30. 


FIG.  29.— Caudal  tendon  of  young  rat,  showing  the  arrangement,  form,  and  structure  of  the  ten- 
don cells,  x  300.  (Klein.) 

FIG.  30. — Transverse  section  of  tendon  from  a  cross-section  of  the  tail  of  a  rabbit,  showing  sheath, 
fibrous  septa,  and  branched  connective-tissue  corpuscles.  The  spaces  left  white  in  the  drawing  rep- 
resent the  tendinous  fibres  in  transverse  section,  x  250.  (Klein.) 

The  rows  of  cells  are  separated  from  one  another  by  lines  of  cement  sub- 
stance. The  cell  spaces  can  be  brought  into  view  by  silver  nitrate.  The 
cells  are  generally  marked  by  one  or  more  lines  or  stripes  when  viewed 
longitudinally.  This  appearance  is  really  produced  by  the  laminar  ex- 
tension either  projecting  upward  or  downward. 

(c.)   Yellow  Elastic  Tissiie. 

Distribution. — In  the  ligamentum  nuchse  of  the  ox,  horse,  and  many 
other  animals;  in  the  ligamenta  subflava  of  man;  in  the  arteries,  consti- 
tuting the  fenestrated  coat  of  Henle;  in  veins;  in  the  lungs  and  trachea; 
in  the  stylo-hyoid,  thyro-hyoid,  and  crico-thyroid  ligaments;  in  the  true 
vocal  cords. 

Structure. — Elastic  tissue  occurs  in  various  forms,  from  a  structure- 
less, elastic  membrane  to  a  tissue  whose  chief  constituents  are  bundles  of 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


33 


elastic  fibres  crossing  each  other  at  different  angles:  these  varieties  may 
be  classified  as  follows: — 

(a.)  Fine  elastic  fibrils,  which  branch  and  anastomose  to  form  a  net- 
work: this  variety  of  elastic  tissue  occurs  chiefly  in  the  skin  and  mucous 
membranes,  in  subcutaneous  and  submucous  tissue,  in  the  lungs  and  true, 
vocal  cords. 

(b.)  Thick  fibres,  sometimes  cylindrical,  sometimes  flattened  like  tape, 
which  branch  and  form  a  network:  these  are  'seen  most  typically  in  the 
ligcimenta  subflava  and  also  in  the  ligamentum  nuchae  of  such  animals  as 
the  ox  and  horse,  in  which  it  is  largely  developed. 

(c.)  Elastic  membranes  with  perforations,  e.g.,  Henle's  fenestrated 
membrane:  this  variety  is  found  chiefly  in  the  arteries  and  veins. 

(d.)  Continuous,   homogeneous  elastic   membranes,    e.g.,   Bowman's 


FIG.  31.  FIG.  32. 

FIG.  31.— Tissue  of  the  jelly  of  Wharton  from  umbilical  cord.  a.  connective-tissue  corpuscles; 
b.  fasciculi  of  connective  tissue;  c.  spherical  formative  cells.  (Frey.) 

FIG.  32. — Part  of  a  section  of  a  lymphatic  gland,  from  which  the  corpuscles  have  been  for  the 
most  part  removed,  showing  the  adenoid  recticulum.  (Klein  and  Noble  Smith.) 

anterior  elastic  lamina,  and  Descemet's  posterior  elastic  lamina,  both  in 
the  cornea. 

A  certain  number  of  flat  connective  tissue  cells  are  found  in  the 
ground  substance  between  the  elastic  fibres  constituting  this  variety  of 
connective  tissue. 

B. — Special  Forms.— (a.)  Gelatinous  Tissue. 

Distribution. — Gelatinous  connective  tissue  forms  the  chief  part  of 
the  bodies  of  jelly  fish;  it  is  found  in  many  parts  of  the  human  embryo, 
but  remains  in  the  adult  only  in  the  vitreous  humor  of  the  eye.  '  It  may 
be  best  seen  in  the  last-named  situation,  in  the  "Whartonian  jelly"  of  the 
umbilical  cord,  and  in  the  enamel  organ  of  developing  teeth. 
VOL.  I.— 3. 


34  HAND-BOOK    OF    PHYSIOLOGY. 

Structure. — It  consists  of  cells,  which  in  the  vitreous  humor  are 
rounded,  and  in  the  jelly  of  the  enamel  organ  are  stellate,  imbedded  in  a 
soft  jelly-like  intercellular  substance  which  forms  the  bulk  of  the  tissue, 
and  which  contains  a  considerable  quantity  of  mucin.  In  the  umbilical 
cord,  that  part  of  the  jelly  immediately  surrounding  the  stellate  cells 
shows  marks  of  obscure  fibrillation. 

(b.)  Adenoid  or  Retiform. 

Distribution. — It  composes  the  stroma  of  the  spleen  and  lymphatic 
glands,  and  is  found  also  in  the  thymus,  in  the  tonsils,  in  the  follicular 
glands  of  the  tongue,  in  Peyer's  patches  and  in  the  solitary  glands  of  the 
intestines,  and  in  the  mucous  membranes  generally. 

Structure. — Adenoid  or  retiform  tissue  consists  of  a  very  delicate  net- 
work of  minute  fibrils,  formed  originally  by  the  union  of  processes  of 
branched  connective-tissue  corpuscles  the  nuclei  of  which,  however,  are 
visible  only  during  the  early  periods  of  development  of  the  tissue 
(Fig.  32). 

The  nuclei  found  on  the  fibrillar  meshwork  do  not  form  an  essential 
part  of  it.  The  fibrils  are  neither  white  fibrous  nor  elastic  tissue,  as  they 
are  insoluble  in  boiling  water,  although  readily  soluble  in  hot  alkaline 
solutions. 

(c.)  Neuroglia. — This  tissue  forms  the  support  of  the  Nervous  ele- 
ments in  the  Brain  and  Spinal  cord.  It  consists  of  a  very  fine  meshwork 
of  fibrils,  said  to  be  elastic,  and  with  nucleated  plates  which  constitute 
the  connective-tissue  corpuscles  imbedded  in  it. 


Fio.  33.— Portion  of  the  submucous  tissue  of  gravid  uterus  of  sow.    a,  branched  cells,  more  or  less 
spindle-shaped;  6.  bundles  of  connective  tissue.    (Klein.) 

Development  of  Fibrous  Tissues. — In  the  embryo  the  place  of 
the  fibrous  tissues  is  at  first  occupied  by  a  mass  of  roundish  cells,  derived 
from  the  "mesoblast." 

These  develop  either  into  a  network  of  branched  cells,  or  into  groups 
of  fusiform  cells  (Fig.  33). 

The  cells  are  imbedded  in  a  semi-fluid  albuminous  substance  derived 
either  from  the  cells  themselves  or  from  the  neighboring  blood-vessels; 
this  afterward  forms  the  cement  substance.  In  it  fibres  are  developed, 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  35 

either  by  part  of  the  cells  becoming  fibrils,  the  others  remaining  as  con- 
nective-tissue corpuscles,  or  by  the  fibrils  being  developed  from  the  out- 
side layers  of  the  protoplasm  of  the  cells,  which  grow  up  again  to  their 
original  size  and  remain  imbedded  among  the  fibres.  This  process  gives 
rise  to  fibres  arranged  in  the  one  case  in  interlacing  networks  (areolar 
tissue),  in  the  other  in  parallel  bundles  (white  fibrous  tissue).  In  the 
mature  forms  of  purely  fibrous  tissue  not  only  the  remnants  of  the  cell- 
substance,  but  even  the  nuclei  may  disappear.  The  embryonic  tissue, 
from  which  elastic  fibres  are  developed,  is  composed  of  fusiform  cells,  and 
a  structureless  intercellular  substance  by  the  gradual  fibrillation  of  which 
elastic  fibres  are  formed.  The  fusiform  cells  dwindle  in  size  and  event- 
ually disappear  so  completely  that  in  mature  elastic  tissue  hardly  a  trace 
of  them  is  to  be  found:  meanwhile  the  elastic  fibres  steadily  increase  in 
size. 

Another  theory  of  the  development  of  the  connective-tissue  fibrils 
supposes  that  they  arise  from  deposits  in  the  intercellular  substance  and 
not  from  the  cells  themselves;  these  deposits,  in  the  case  of  elastic  fibres, 
appearing  first  of  all  in  the  form  of  rows  of  granules,  which,  joining 
together,  form  long  fibrils.  It  seems  probable  that  even  if  this  view  be 
correct,  the  cells  themselves  have  a  considerable  influence  in  the  produc- 
tion of  the  deposits  outside  them. 

Functions  of  Areolar  and  Fibrous  Tissue. — The  main  function 
of  connective  tissue  is  mechanical  rather  than  vital:  it  fulfils  the  subsidi- 
ary but  important  use  of  supporting  and  connecting  the  various  tissues 
and  organs  of  the  body. 

In  glands  the  trabeculae  of  connective  tissue  form  an  interstitial  frame- 
work in  which  the  parenchyma  or  secreting  gland-tissue  is  lodged:  in 
muscles  and  nerves  the  septa  of  connective  tissue  support  the  bundles  of 
fibres,  which  form  the  essential  part  of  the  structure. 

Elastic  tissue,  by  virtue  of  its  elasticity,  has  other  important  uses: 
these,  again,  are  mechanical  rather  than  vital.  ^  Thus  the  ligamentum 
nuchas  of  the  horse  or  ox  acts  very  much  as  an  India-rubber  band  in  the 
same  position  would.  It  maintains  the  head  in  a  proper  position  without 
any  muscular  exertion;  and  when  the  head  has  been  lowered  by  the  action 
of  the  flexor  muscles  of  the  neck,  and  the  ligamentum  nuchae  thus 
stretched,  the  head  is  brought  up  again  to  its  normal  position  by  the 
relaxation  of  the  flexor  muscles  which  allows  the  elasticity  of  the  liga- 
mentum nuchae  to  come  again  into  play. 

(a.)  Adipose  Tissue. 

Distribution. — In  almost  all  regions  of  the  human  body  a  larger  or 
smaller  quantity  of  adipose  or  fatty  tissue  is  present;  the  chief  exceptions 
being  the  subcutaneous  tissue  of  the  eyelids,  penis,  and  scrotum,  the 
nymphae,  and  the  cavity  of  the  cranium.  Adipose  tissue  is  also  absent 
from  the  substance  of  many  organs,  as  the  lungs,  liver,  and  others. 


36  HAND-BOOK    OF    PHYSIOLOGY. 

Fatty  matter,  not  in  the  form  of  a  distinct  tissue,  is  also  widely  pres- 
ent in  the  body,  e.g.,  in  the  liver  and  brain,  and  in  the  blood  and  chyle. 

Adipose  tissue  is  almost  always  found  seated  in  areolar  tissue,  and  forms 
in  its  meshes  little  masses  of  unequal  size  and  irregular  shape,  to  which 
the  term  lobules  is  commonly  applied. 

Structure. — Under  the  microscope  adipose  tissue  is  found  to  consist 
essentially  of  little  vesicles  or  cells  which  present  dark,  sharply-defined 
edges  when  viewed  with  transmitted  light:  they  are  about  j-J-g-  or  ^w  of 
an  inch  in  diameter,  each  composed  of  a  structureless  and  colorless  mem- 
brane or  bag,  filled  with  fatty  matter,  which  is  liquid  during  life,  but  in 
part  solidified  after  death  (Fig.  34).  A  nucleus  is  always  present  in  some 
part  or  other  of  the  cell- wall,  but  in  the  ordinary  condition  of  the  cell  it 
is  not  easily  or  always  visible. 


FIG.  34.  FIG.  35. 

FIG.  34. — Ordinary  fat-cells  of  a  fat  tract  in  the  omentum  of  a  rat.    (Klein.) 
FIG.  33.— Group  of  fat-cells  (TO)  with  capillary  vessels  (c).    (Noble  Smith.) 

This  membrane  and  the  nucleus  can  generally  be  brought  into  view  by 
staining  the  tissue:  it  can  be  still  more  satisfactorily  demonstrated  by  ex- 
tracting the  contents  of  the  fat-cells  with,  ether,  when  the  shrunken, 
shriveled  membranes  remain  behind.  By  mutual  pressure,  fat-cells  come 
to  assume  a  polyhedral  figure  (Fig.  35). 

The  ultimate  cells  are  held  together  by  capillary  blood-vessels  (Fig. 
35);  while  the  little  clusters  thus  formed  are  grouped  into  small  masses, 
and  held  so,  in  most  cases,  by  areolar  tissue. 

The  oily  matter  contained  in  the  cells  is  composed  chiefly  of  the  com- 
pounds of  fatty  acids  with  glycerin,  which  are  named  olein,  stearin,  and 
palmitin. 

Development  of  Adipose  Tissue. — Fat-cells  are  developed  from 
connective- tissue  corpuscles:  in  the  infra-orbital  connective-tissue  cells 
may  be  found  exhibiting  every  intermediate  gradation  between  an  ordi- 
nary branched  connective-tissue  corpuscle  and  a  mature  fat-cell.  The 
process  of  development  is  as  follows:  a  few  small  drops  of  oil  make  their 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


37 


appearance  in  the  protoplasm:  by  their  confluence  a  larger  drop  is  pro- 
duced (Fig.  37):  this  gradually  increases  in  size  at  the  expense  of  the  orig- 
inal protoplasm  of  the  cell,  which  becomes  correspondingly  diminished 
in  quantity  till  in  the  mature  cell  it  only  forms  a  thin  crescentic  film, 
•closely  pressed  against  the  cell-wall,  and  with  a  nucleus  imbedded  in  its 
substance  (Figs.  34  and  37). 

Under  certain  circumstances  this  process  may  be  reversed  and  fat -cells 
may  be  changed  back  into  connective-tissue  corpuscles.     (Kolliker,  Yir- 

<3llOW. 


FIG.  36.  FIG.  37. 

FIG.  36.— Blood-vessels  of  adipose  tissue.  A.  Minute  flattened  fat-lobule,  in  which  the  vessels  only 
represented,  a,  the  terminal  artery;  v,  the  primitive  vein;  6,  the  fat  vesicles  of  one  border  of 
le  lobule  separately  represented.  X  100.  B.  Plan  of  the  arrangement  of  the  capillaries  (c)  on  the 
cterior  of  the  vesicles:  more  highly  magnified.  (Todd  and  Bowman.) 

FIG.  37. — A  lobule  of  developing  adipose  tissue  from  an  eight  months'1  foetus,  a.  Spherical,  or, 
from  pressure,  polyhedral  cells  with  large  central  nucleus,  surrounded  by  a  finely  reticulated  sub- 
stance staining  uniformly  with  haematpxylin.  b.  Similar  cells  with  spaces  from  which  the  fat  has 
been  removed  by  oil  of  cloves,  c.  Similar  cells  showing  how  the  nucleus  with  enclosing  protoplasm 
is  being  pressed  towards  periphery,  d.  Nucleus  of  endothelium  of  investing  capillaries.  (McCarthy.) 
Drawn  by  Treves. 

Vessels  and  Nerves. — A  large  number  of  blood-vessels  are  found  in 
adipose  tissue,  which  subdivide  until  each  lobule  of  fat  contains  a  fine 
mesh  work  of  capillaries  ensheathing  each  individual  fat-globule.  Al- 
though nerve  fibres  pass  through  the  tissue,  no  nerves  have  been  demon- 
strated to  terminate  in  it. 

The  Uses  of  Adipose  Tissue. — Among  the  uses  of  adipose  tissue, 
these  are  the  chief: — 

a.  It  serves  as  a  store  of  combustible  matter  which  may  be  re-ab- 
sorbed into  the  blood  when  occasion  requires,  and,  being  burnt,  may 
help  to  preserve  the  heat  of  the  body. 

I.  That  part  of  the  fat  which  is  situate  beneath  the  skin  must,  by  its 
want  of  conducting  power,  assist  in  preventing  undue  waste  of  the  heat 
-of  the  body  by  escape  from  the  surface. 


HAND-BOOK    OF    PHYSIOLOGY. 

6'.  As  a  packing  material,  fat  serves  very  admirably  to  fill  up  spaces, 
to  form  a  soft  and  yielding  yet  elastic  material  wherewith  to  wrap  tender 
and  delicate  structures,  or  form  a  bed  with  like  qualities  on  which  such 
structures  may  lie,  not  endangered  by  pressure. 

As  good  examples  of  situations  in  which  fat  serves  such  purposes  may 
be  mentioned  the  palms  of  the  hands  and  soles  of  the  feet,  and  the  orbits. 


FIG.  38. — Branched  connective-tissue  corpuscles,  developing  into  fat-cells.    (Klein. ) 

d.  In  the  long  bones,  fatty  tissue,  in  the  form  known  as  yellow  mar- 
row, fills  the  medullary  canal,  and  supports  the  small  blood-vessels  which 
are  distributed  from  it  to  the  inner  part  of  the  substance  of  the  bone. 

II.    CAKTILAGE. 

Cartilage  or  gristle  exists  in  three  different  forms  in  the  human  body,, 
yiz.,  1,  Hyaline  cartilage,  2,  Yellow  elastic  cartilage,  and  3,  White  fibro- 
cartilage. 

Structure  of  Cartilage. — All  kinds  of  cartilage  are  composed  of 
cells  imbedded  in  a  substance  called  the  matrix :  and  the  apparent  differ- 
ences of  structure  met  with  in  the  various  kinds  of  cartilage  are  more  due 
to  differences  in  the  character  of  the  matrix  than  of  the  cells.  Among 
the  latter,  however,  there  is  also  considerable  diversity  of  form  and  size. 

With  the  exception  of  the  articular  variety,  cartilage  is  invested  by  a 
thin  but  tough  firm  fibrous  membrane  called  the  pericliondrium.  On  the 
surface  of  the  articular  cartilage  of  the  foetus,  the  pericliondrium  is  rep- 
resented by  a  film  of  epithelium;  but  this  is  gradually  worn  away  up  to- 
the  margin  of  the  articular  surfaces,  when  by  use  the  parts  begin  to  suffer 
friction. 

Nerves  are  probably  not  supplied  to  any  variety  of  cartilage. 

1.  Hyaline  Cartilage. 

Distribution. — This  variety  of  cartilage  is  met  with  largely  in  the 
human  body — investing  the  articular  ends  of  bones,  and  forming  the 
costal  cartilages,  the  nasal  cartilages,  and  those  of  the  larynx  with  the  ex- 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


39 


The  cartilages  of  the 


ception  of  the  epiglottis  and  cornicula  laryngis. 
trachea  and  bronchi  are  also  hyaline. 

Mr  net  lire.—  Like  other  cartilages  it  is  composed  of  cells  imbedded  in 
a  matrix.  The  cells,  which  contain  a  nucleus  with  nucleoli,  are  irregular 
in  sTiape,  and  generally  grouped  together 
in  patches  (Fig.  39).  The  patches  are 
of  various  shapes  and  sizes,  and  placed 
at  unequal  distances  apart.  They  gen- 
erally appear  flattened  near  the  free  sur- 
face of  the  mass  of  cartilage  in  which 
they  are  placed,  and  more  or  less  per- 
pendicular to  the  surface  in  the  more- 
deeply  seated  portions. 

The  matrix  of  hyaline  cartilage  has 
a  dimly  granular  appearance  like  that  of 
ground  glass,  and  in  man  and  the  higher 
animals  has  no  apparent  structure.  In 
some  cartilages  of  the  frog,  however, 
even  when  examined  in  the  fresh  state, 
it  is  seen  to  be  mapped  out  into  polygo- 
nal blocks  or  cell-territories,  each  con- 
taining a  cell  in  the  centre,  and  representing  what  is  generally  called 
the  capsule  of  the  cartilage  cells  (Fig.  40).  Hyaline  cartilage  in  man 
has  really  the  same  structure,  which  can  be  demonstrated  by  the  use  of 
certain  reagents.  If  a  piece  of  human  hyaline  cartilage  be  macerated 


-^ 

FIG.  39.— Ordinary  hyaline  cartilage  from 
trachea  of  a  child.  The  cartilage  cells  are 
enclosed  singly  or  in  pairs  in  a  capsule  of 
hyaline  substance.  X  150  diams.  (Klein 
and  Noble  Smith.) 


FIG.  40.— Fresh  cartilage  from  the  Triton.    (A.  Rollett.) 

for  a  long  time  in  dilute  acid  or  in  hot  water  95°— 113°  F.  (35°  to 
45°  C.),  the  matrix,  which  previously  appeared  quite  homogeneous,  is 
found  to  be  resolved  into  a  number  of  concentric  lamellae,  like  the  coats 


40  HAND-BOOK    OF    PHYSIOLOGY. 

of  an  onion,  arranged  round  each  cell  or  group  of  cells.  It  is  thus 
shown  to  consist  of  nothing  but  a  number  of  large  systems  of  capsules 
which  have  become  fused  with  one  another 

The  cavities  in  the  matrix  in  which  the  cells  lie  are  connected  to- 
gether by  a  series  of  branching  canals,  very  much  resembling  those  in  the 
cornea:  through  these  canals  fluids  may  make  their  way  into  the  depths 
of  the  tissue. 

In  the  hyaline  cartilage  of  the  ribs,  the  cells  are  mostly  larger  than  in 
the  articular  variety,  and  there  is  a  tendency  to  the  development  of  fibres 
in  the  matrix.  The  costal  cartilages  also  frequently  become  calcified  in 
old  age,  as  also  do  some  of  those  of  the  larynx.  Fat-globules  may  .also  be 
seen  in  many  cartilages. 

In  articular  cartilage  the  cells  are  smaller,  and  arranged  vertically  in 
narrow  lines  like  strings  of  beads. 

Temporary  Cartilage.— In  the  foetus,  cartilage  is  the  material  of 
which  the  bones  are  first  constructed;  the  "model"  of  each  bone  being 
laid  down,  so  to  speak,  in  this  substance.  In  such  cases  the  cartilage  is 
termed  temporary.  It  closely  resembles  the  ordinary  hyaline  kind;  the 
cells,  however,  are  not  grouped  together  after  the  fashion  just  described, 
but  are  more  uniformly  distributed  throughout  the  matrix. 

A  variety  of  temporary  hyaline  cartilage  which  has  scarcely  any  matrix 
is  found  in  the  human  subject  only  in  early  foetal  life,  when  it  constitutes 
the  chorda  dorsalis. 

Nutrition  of  Cartilage. — Hyaline  cartilage  is  reckoned  among  the 
so-called  non-vascular  structures,  no  blood-vessels  being  supplied  directly 
to  its  own  substance;  it  is  nourished  by  those  of  the  bone  beneath. 
When  hyaline  cartilage  is  in  thicker  masses,  as  in  the  case  of  the  cartilages 
of  the  ribs,  a  few  blood-vessels  traverse  its  substance.  The  distinction, 
howeyer,  between  all  so-called  vascular  and  non-vascular  parts,  is  at  the 
best  a  very  artificial  one. 

2.  Yellow  Elastic  Cartilage. 

Distribution. — In  the  external  ear,  in  the  epiglottis  and  cornicula 
laryngis,  and  in  the  Eustachian  tube. 

Structure. — The  cells  are  rounded  or  oval,  with  well-marked  nuclei 
and  nucleoli  (Fig.  41).  The  matrix  in  which  they  are  seated  is  composed 
almost  entirely  of  fine  elastic  fibres,  which  form  an  intricate  interlace- 
ment about  the  cells,  and  in  their  general  characters  are  allied  to  the  yel- 
low variety  of  fibrous  tissue:  a  small  and  variable  quantity  of  hyaline  in- 
tercellular substance  is  also  usually  present. 

A  variety  of  elastic  cartilage,  sometimes  called  cellular,  may  be  obtained 
from  the  external  ear  of  rats,  mice,  or  other  small  mammals.  It  is  com- 
posed almost  entirely  of  cells  (hence  the  name),  which  are  packed  very 
closely,  with  little  or  no  matrix.  When  present  the  matrix  consists  of 


STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.  41 

very  fine  fibres,  which  twine  about  the  cells  in  various  directions  and 
enclose  them  in  a  kind  of  network. 


3.  White  Fibro-Cartilage. 

Distribution. — The  different  situations  in  which  white  fibro -cartilage 
is  found  have  given  rise  to  the  following  classification: — 

1.  Inter-articular  nbro-cartilage,  e.g.,  the  semilunar  cartilages  of 
the  knee-joint. 


FIG.  41. 


FIG.  42. 


FIG.  41.— Section  of  the  epiglottis.    (Baly.) 

FIG.  42.— Tranverse  section  through  the  intervertebral  cartilage  of  the  tail  of  mouse,  showing 
lamellse  of  fibrous  tissue  with  cartilage  cells  arranged  in  rows  between  them.  The  cells  are  seen  in 
profile,  and  being  flattened,  appear  staff-shaped.  Each  cell  lies  in  a  capsule.  X  350.  (Klein  and 
Noble  Smith.) 

2.  Circumferential  or  marginal,  as  on  the  edges  of  the  acetabulum 
and  glenoid  cavity. 

3.  Connecting,  e.g.,  the  inter-vertebral  fibro-cartilages. 

4.  In  the  sheaths  of  tendons,  and  sometimes  in  their  substance.     In 
the  latter  situation,  the  nodule  of  fibro-cartilage  is  called  a  sesamoid  fibro- 
cartilage,   of  which  a  specimen   may  be 

found  in  the  tendon  of  the  tibialis  posti- 
cus,  in  the  sole  of  the  foot,  and  usually 
in  the  neighboring  tendon  of  the  peroneus 
longus. 

Structure. — White  fibro-cartilage  (Fig. 
43),  which  is  much  more  widely  distribu- 
ted throughout  the  body  than  the  forego- 
ing kind,  is  composed,  like  it,  of  cells  and 
a  matrix;  the  latter,  however,  being  made 
up  almost  entirely  of  fibres  closely  resem- 
bling those  of  white  fibrous  tissue. 

In  this  kind  of  fibro-cartilage  it  is  not 
unusual  to  find  a  great  part  of  rfcs  mass 
composed  almost  exclusively  of  fibres,  and  deriving  the  name  of  cartilage 
only  from  the  fact  that  in  another  portion,  continuous  with  it,  cartilage 
cells  may  be  pretty  freely  distributed. 


FIG.  43.— White  fibro-cartilage  from 
an  intervertebral  ligament.  (Klein  and 
Noble  Smith.) 


4'2  HAND-BOOK    OF    PHYSIOLOGY 

Functions  of  Cartilage. — Cartilage  not  only  represents  in  the  foetus 
the  bones  which  are  to  be  formed  (temporary  cartilage),  but  also  offers  a 
firm,  but  more  or  less  yielding,,  framework  for  certain  parts  in  the  de- 
veloped body,  possessing  at  the  same  time  strength  and  elasticity.  It 
maintains  the  shape  of  tubes  as  in  the  larynx  and  trachea.  It  affords 
attachment  to  muscles  and  ligaments;  it  binds  bones  together,  yet  allows 
a  certain  degree  of  movement,  as  between  the  vertebrae;  it  forms  a  firm 
framework  and  protection,  yet  without  undue  stiffness  or  weight,  as  in 
the  pinna,  larynx,  and  chest  walls;  it  deepens  joint  cavities,  as  in  the 
acetabulum,  without  unduly  restricting  the  movements  of  the  bones. 

Development  of  Cartilage. — Cartilage  is  developed  out  of  an  em- 
bryonal tissue,  consisting  of  cells  with  a  very  small  quantity  of  intercel- 
lular substance:  the  cells  multiply  by  fission  within  the  cell-capsules  (Fig. 
6) ;  while  the  capsule  of  the  parent  cell  becomes  gradually  fused  with  the 
surrounding  intercellular  substance.  A  repetition  of  this  process  in  the 
young  cells  causes  a  rapid  growth  of  the  cartilage  by  the  multiplication 
of  its  cellular  elements  and  corresponding  increase  in  its  matrix. 

III.  BO^E. 

Chemical  Composition. — Bone  is  composed  of  earthy  and  animal 
matter  in  the  proportion  of  about  67  per  cent,  of  the  former  to  33  per 
cent,  of  the  latter.  The  earthy  matter  is  composed  chiefly  of  calcium 
phosphate,  but  besides  there  is  a  small  quantity  (about  11  of  the  67  per 
cent.)  of  calcium  carbonate  and  fluoride,  and  magnesium  phosphate. 

The  animal  matter  is  resolved  into  gelatin  by  boiling. 

The  earthy  and  animal  constituents  of  bone  are  so  intimately  blended 
and  incorporated  the  one  with  the  other,  that  it  is  only  by  chemical 
action,  as,  for  instance,  by  heat  in  one  case  and  by  the  action  of  acids 
in  another,  that  they  can  be  separated.  Their  close  union,  too,  is  further 
shown  by  the  fact  that  when  by  acids  the  earthy  matter  is  dissolved  out, 
or,  on  the  other  hand,  when  the  animal  part  is  burnt  out,  the  shape  of 
the  bone  is  alike  preserved. 

The  proportion  between  these  two  constituents  of  bone  varies  in  dif- 
ferent bones  in  the  same  individual,  and  in  the  same  bone  at  different 


Structure. — To  the  naked  eye  there  appear  two  kinds  of  structure  in 
diiferent  bones,  and  in  different  parts  of  the  same  bone,  namely,  the  dense 
or  compact,  and  the  spongy  or  cancellous  tissue. 

Thus,  in  making  a  longitudinal  section  of  a  long  bone,  as  the  humerus 
or  femur,  the  articular  extremities  are  found  capped  on  their  surface  by 
a  thin  shell  of  compact  bone,  while  their  interior  is  made  up  of  the 
spongy  or  cancellous  tissue.  The  shaft,  on  the  other  hand,  is  formed 
almost  entirely  of  a  thick  layer  of  the  compact  bone,  and  this  surrounds 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  43 

a  central  canal,  the  medullary  cavity — so  called  from  its  containing  the 
•medulla  or  marrow. 

In  the  flat,  bones,  as  the  parietal  bone  or  the  scapula,  one  layer  of  the 
cancellous  structure  lies  between  two  layers  of  the  compact  tissue,  and 
in  the  short  and  irregular  bones,  as  those  of  the  carpus  and  tarsus,  the 
cancellous  tissue  alone  fills  the  interior,  while  a  thin  shell  of  compact 
bone  forms  the  outside. 

Marrow. — There  are  two  distinct  varieties  of  marrow — the  red  and 
yelloiv. 

Red  marrow  is  that  variety  which  occupies  the  spaces  in  the  cancel- 
lous tissue;  it  is  highly  vascular,  and  thus  maintains  the  nutrition  of  the 
spongy  bone,  the  interstices  of  which  it  fills.  It  contains  a  few  fat-cells 
and  a  large  number  of  marrow-cells,  many  of  which  are  undistinguishable 


FIG.  44. — Cells  of  the  red  marrow  of  the  guinea  pig,  highly  magnified,    a,  a  large  cell,  the  nucleus 
partly  divided  into  three  by  constrictions;  6,  a  < 
being  constricted  into  a  number  of  smaller  nuclei ;  c,  a  so-called  giant  cell, 

1UC" 

marrow.    (E.  A.  Schiifer.) 


of  which  appears  to  be  partly  divided  into  three  by  constrictions;  6,  a  cell,  the  nucleus  of  which 
shows  an  appearance  of  being  constricted  into  a  number  of  smaller  nuclei;  c,  a  so-called  giant  cell, 
or  myeloplaxe.with  many  nuclei ;  d,  a  smaller  myeloplaxe,  with  thr^  nuclei ;  e — t,  proper  cells  of  the 


from  lymphoid  corpuscles,  and  has  for  a  basis  a  small  amount  of  fibrous 
tissue.  Among  the  cells  are  some  nucleated  cells  of  very  much  the  same 
tint  as  colored  blood-corpuscles.  There  are  also  a  few  large  cells  with. 
many  nuclei,  termed  "giant-cells"  (myeloplaxes)  which  are  derived  from 
over-growth  of  the  ordinary  marrow-cells  (Fig.  44). 

Yelloio  marrow  fills  the  medullary  cavity  of  long  bones,  and  consists 
chiefly  of  fat-cells  with  numerous  blood-vessels;  many  of  its  cells  also  are 
in  every  respect  similar  to  lymphoid  corpuscles. 

From  these  marrow-cells,  especially  those  of  the  red  marrow,  are 
derived,  as  we  shall  presently  show,  large  quantities  of  red  blood-cor- 
puscles. 

Periosteum  and  Nutrient  Blood-vessels. — The  surfaces  of  bones, 
except  the  part  covered  with  articular  cartilage,  are  clothed  by  a  tough, 
fibrous  membrane,  the  periosteum;  and  it  is  from  the  blood-vessels  which 
are  distributed  in  this  membrane,  that  the  bones,  especially  their  more 
compact  tissue,  are  in  great  part  supplied  with  nourishment, — minute 


44  HAND-BOOK    OF    PHYSIOLOGY. 

branches  from  the  periosteal  vessels  entering  the  little  foramina  on  the 
surface  of  the  bone,  and  finding  their  way  to  the  Haversian  canals,  to  be 
immediately  described.  The  long  bones  are  supplied  also  by  a  proper 
nutrient  artery  which,  entering  at  some  part  of  the  shaft  so  as  to  reach 
the  medullary  canal,  breaks  up  into  branches  for  the  supply  of  the  mar- 
row, from  which  again  small  vessels  are  distributed  to  the  interior  of  the 
bone.  Other  small  blood-vessels  pierce  the  articular  extremities  for  the 
supply  of  the  cancellous  tissue. 

Microscopic  Structure  of  Bone. — Notwithstanding  the  differences 
of  arrangement  just  mentioned,  the  structure  of  all  bone  is  found  under 
the  microscope  to  be  essentially  the  same. 


FIG.  45. — Transverse  section  of  compact  bony  tissue  (of  humerus).  Three  of  the  Haversian 
canals  are  seen,  with  their  concentric  rings;  also  the  corpuscles  or  lacunae,  with  the  canaliculi  extend- 
ing from  them  across  the  direction  of  the  lamellae.  The  Haversian  apertures  had  got  filled 
with  debris  in  grinding  down  the  section,  and  therefore  appear  black  in  the  figure,  which  represents 
the  object  as  viewed  with  transmitted  light.  The  Haversian  systems  are  so  closely  packed  in  this 
section,  that  scarcely  any  interstitial  lamella?  are  visible.  X  150.  (Sharpey.) 

Examined  with  a  rather  high  power  its  substance  is  found  to  contain 
a  multitude  of  little  irregular  spaces,  approximately  fusiform  in  shape, 
called  lacuncB,  with  very  minute  canals  or  canaliculij  as  they  are  termed, 
leading  from  them,  and  anastomosing  Avith  similar  little  prolongations 
from  other  lacunae  (Fig.  45).  In  very  thin  layers  of  bone,  no  other  canals 
than  these  may  be  visible;  but  on  making  a  transverse  section  of  the 
compact  tissue  as  of  a  long  bone,  e.g.,  the  humerus  or  ulna,  the  arrange- 
ment shown  in  Fig.  45  can  be  seen. 

The  bone  seems  mapped  out  into  small  circular  districts,  at  or  about 
the  centre  of  each  of  which  is  a  hole,  and  around  this  an  appearance  as 
of  concentric  layers — the  lacunce  and  canaliculi  following  the  same  con- 
centric plan  of  distribution  around  the  small  hole  in  the  centre,  with 
"which,  indeed,  they  communicate. 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


45 


On  making  a  longitudinal  section,  the  central  holes  are  found  to  be 
simply  the  cut  extremities  of  small  canals  which  run  lengthwise  through 
the  bone,  anastomosing  with  each  other  by  lateral  branches  (Fig.  4G), 
and  are  called-  Haversian  canals,  after  the  name  of  the  physician,  Cloptoa 
Havers,  who  first  accurately  described  them.  The  Haversian  canals,  the 
average  diameter  of  which  is  -^-^  of  an  inch,  contain  blood-vessels,  and 
by  means  of  them  blood  is  conveyed  to  all,  even  the  densest  parts  of  the 
bone;  the  minute  canaliculi  and  lacunae  absorbing  nutrient  matter  from 
the  Haversian  blood-vessels,  and  conveying  it  still  more  intimately  to  the 
very  substance  of  the  bone  which  they  traverse. 

The  blood-vessels  enter  the  Haversian  canals  both  from  without,  by 


FIG.  46. 


FIG.  46.— Longitudinal  section  of  human  ulna,  showing  Haversian  canal,  lacunae,  and  canaliculi. 
FIG.  47. — Bone  corpuscles  with  their  processes  as  seen  hi  a  thin  section  of  human  bone.  (Rollett.) 

traversing  the  small  holes  which  exist  on  the  surface  of  all  bones  beneath 
the  periosteum,  and  from  within  by  means  of  small  channels  which 
extend  from  the  medullary  cavity,  or  from  the  cancellous  tissue.  The 
arteries  and  veins  usually  occupy  separate  canals,  and  the  veins,  which 
are  the  larger,  often  present,  at  irregular  intervals,  small  pouch-like 
dilatations. 

The  lacuncB  are  occupied  by  branched  cells  (bone-cells,  or  bone-cor- 
puscles) (Fig.  47),  which  very  closely  resemble  the  ordinary  branched 
connective-tissue  corpuscles;  each  of  these  little  masses  of  protoplasm 
ministering  to  the  nutrition  ol  the  bone  immediately  surrounding  it, 
and  one  lacunar  corpuscle  communicating  with  another,  and  with  its  sur- 
rounding district,  and  with  the  blood-vessels  of  the  Haversian  canals,  by 


46  HAND-BOOK    OF    PHYSIOLOGY. 

means  of  the  minute  streams  of  fluid  nutrient  matter  which  occupy  the 
canaliculi. 

It  will  be  seen  from  the  above  description  that  bone  is  essentially  con- 
nective-tissue impregnated  with  lime  salts:  it  bears  a  very  close  resem- 
blance to  what  may  be  termed  typical  connective-tissue  such  as  the 
substance  of  the  cornea.  The  bone-corpuscles  with  tTieir  processes,  occu- 
pying the  lacunae  and  canaliculi,  correspond  exactly  to  the  cornea-cor- 
puscles lying  in  branched  spaces;  while  the  finely  fibrillated  structure  of 
the  bone-lamellae,  to  be  presently  described,  resembles  the  fibrillated  sub- 
stance of  the  cornea  in  which  the  branching  spaces  lie. 

Lamellae  of  Compact  Bone.  —  In  the  shaft  of  a  long  bone  three 
distinct  sets  of  lamellae  can  be  clearly  recognized. 

(1.)  General  or  fundamental  lamellae;  which  are  most  easily  traceable 
just  beneath  the  periosteum,  and  around  the  medullary  cavity,  forming 
around  the  latter  a  series  of  concentric  rings.  At  a  little  distance  from 
the  medullary  and  periosteal  surfaces  (in  the  deeper  portions  of  the  bone) 
they  are  more  or  less  interrupted  by 

(2.)  Special  or  Haversian  lamellae,  which  are  concentrically  arranged 
around  the  Haversian  canals  to  the  number  of  six  to  eighteen  around 
each. 

(3.)  Interstitial  lamellae,  which  connect   the    systems  of  Haversian 
lamellae,    filling  the  spaces  between  them,   and  consequently  attaining 
their  greatest  development  where  the   Haversian 
systems  are  few,  and  vice  versa. 

The  ultimate  structure  of  the  lamellce  appears 
to  be  reticular.  If  a  thin  film  be  peeled  off  the 
surface  of  a  bone,  from  which  the  earthy  matter  has 
been  removed  by  acid,  and  examined  with  a  high 
power  of  the  microscope,  it  will  be  found  com- 
posed of  a  finely  reticular  structure,  formed  appar- 
ently of  very  slender  fibres  decussating  obliquely, 
but  coalescing  at  the  points  of  intersection,  as  if 
here  the  fibres  were  fused  rather  than  woven 

Fio.  48.—  Thin  layer  peeled  ,,         /T-v        .  m         /0,  x 

off   from  a  softened   bone,     together  (Fig.   48).       (Sharpey.) 
This  figure,  which  is  intend-  T  -,  ,-,  j_-       -i         i  n 

ed  to  represent  the  reticular  In  many  places  these  reticular  lamellae  are 
perforated  by  tapering  fibres  (davictdi  of  Gagli- 
ardi),  resembling  in  character  the  ordinary  white 


400.    (Sharpey.) 

neighboring  lamellae  together,  and  may  be  drawn  out  when  the  latter  are 
torn  asunder  (Fig.  49).  These  perforating  fibres  originate  from  ingrow- 
ing processes  of  the  periosteum,  and  in  the  adult  still  retain  their  con- 
nection with  it. 

Development  of  Bone.  —  From  the  point  of  view  of  their  develop- 
ment, all  bones  may  be  subdivided  into  two  classes. 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  47 

(a.)  Those  which  are  ossified  directly  in  membrane,  e.g.,  the  bones 
forming  the  vault  of  the  skull,  parietal,  frontal. 

(b.)  Those  whose  form,  previous  to  ossification,  is  laid  down  in  Hyaline, 
cartilage,  «.</., 'humerus,  femur. 

The  process  of  development,  pure  and  simple,  may  be  best  studied 
in  bones  which  are  not  preceded  by  cartilage — "membrane-bones"  (e.g., 
parietal);  and  without  a  knowledge  of  this  process  (ossification  in  mem- 
brane), it  is  impossible  to  understand  the  much  more  complex  series  of 


a 

FIG.  49. — Lamellae  torn  off  from  a  decalcified  human  parietal  bone  at  some  depth  from  the  sur- 
face, a,  a  lamella,  showing  reticular  fibres ;  6,  6,  darker  part,  where  several  lamellae  are  superposed ; 
c,  perforating  fibres.  Apertures  through  which  perforating  fibres  had  passed,  are  seen  especially  in 
the  lower  part,  a,  a,  of  the  figure.  (Allen  Thomson.) 

changes  through  which  such  a  structure  as  the  cartilaginous  femur  of  the 
foetus  passes  in  its  transformation  into  the  body  femur  of  the  adult  (ossi- 
fication in  cartilage). 

Ossification  in  Membrane. — The  membrane  or  periosteum  from 
which  such  a  bone  as  the  parietal  is  developed  consists  of  two  layers — an 
external  fibrous,  and  an  internal  cellular  or  osteogenetic. 

The  external  one  consists  of  ordinary  connective-tissue,  being  com- 
posed of  layers  of  fibrous  tissue  with  branched  connective-tissue  corpuscles 
here  and  there  between  the  bundles  of  fibres.  The  internal  layer  consists 
of  a  network  of  fine  fibrils  with  a  large  number  of  nucleated  cells,  some 
of  which  are  oval,  others  drawn  out  into  a  long  branched  process,  and 
others  branched:  it  is  more  richly  supplied  with  capillaries  than  the  outer 
layer.  The  relatively  large  number  of  its  cellular  elements,  their  varia- 
bility in  size  and  shape,  together  with  the  abundance  of  its  blood-vessels, 
clearly  mark  it  out  as  the  portion  of  the  periosteum  which  is  immediately 
concerned  in  the  formation  of  bone. 

In  such  a  bone  as  the  parietal,  the  deposition  of  bony  matter,  which 
is  preceded  by  increased  vascularity,  takes  place  in  radiating  spiculae, 


48  HAND-BOOK    OF    PHYSIOLOGY. 

starting  from  a  "centre  of  ossification,"  and  shooting  out  in  all  directions 
toward  the  periphery;  while  the  bone  increases  in  thickness  by  the  depo- 
sition of  successive  layers  beneath  the  periosteum.  The  finely  fibrillar 
network  of  the  deeper  or  osteogenetic  layer  of  the  periosteum  becomes, 
transformed  into  bone-matrix  (the  minute  structure  of  which  has  been 
already  (p.  46)  described  as  reticular),  and  its  cells  into  bone-corpuscles. 
On  the  young  bone  trabeculaa  thus  formed,  fresh  layers  of  cells  (osteo- 
blasts)  from  the  osteogenetic  layer  are  developed  side  by  side,  lining  the. 
irregular  spaces  like  an  epithelium  (Fig.  50,  1)).  Lime-salts  are  deposited 
in  the  circumferential  part  of  each  osteoblast,  and  thus  a  ring  of  osteo- 
blasts gives  rise  to  a  ring  of  bone  with  the  remaining  uncalcified  portions 
of  the  osteoblasts  imbedded  in  it  as  bone-corpuscles  (Fig.  50). 


FIG.  50.— Osteoblasts  from  the  parietal  bone  of  a  human  embryo,  thirteen  weeks  old.  a,  bony 
septa  with  the  cells  of  the  lacunae;  b,  layers  of  osteoblasts;  c,  the  latter  in  transition  to  bone  cor- 
puscles. Highly  magnified. ,  (Gegenbaur.) 

Thus,  the  primitive  spongy  bone  is  formed,  whose  irregular  branch- 
ing spaces  are  occupied  by  processes  from  the  osteogenetic  layer  of  the 
periosteum  with  numerous  blood-vessels  and  osteoblasts.  Portions  of  this 
primitive  spongy  bone  are  re-absorbed;  the  osteoblasts  being  arranged  in 
concentric  successive  layers  and  thus  giving  rise  to  concentric  Haversian 
lamellae  of  bone,  until  the  irregular  space  in  the  centre  is  reduced  to  a 
well-formed  Haversian  canal,  the  portions  of  the  primitive  spongy  bone 
between  the  Haversian  systems  remaining  as  interstitial  or  ground- 
lamellae  (p.  46).  The  bulk  of  the  primitive  spongy  bone  is  thus  gradu- 
ally converted  into  compact  bony-tissue  with  Haversian  canals.  Those 
portions  of  the  in-growths  from  the  deeper  layer  of  the  periosteum  which 
are  not  converted  into  bone  remain  in  the  spaces  of  the  cancellous  tissue 
as  the  red  marrow. 

Ossification  in  Cartilage. — Under  this  heading,  taking  the  femur  as 
a  typical  example,  we  may  consider  the  process  by  which  the  solid  carti- 
laginous rod  which  represents  it  in  the  foetus  is  converted  into  the  hollow 
cylinder  of  compact  bone  with  expanded  ends  of  cancellous  tissue  which 
forms  the  adult  femur;  bearing  in  mind  the  fact  that  this  foetal  cartilag- 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


49 


inous  femur  is  many  times  smaller  than  the  medullary  cavity  even  of  the 
shaft  of  the  mature  bone,  and,  therefore,  that  not  a  trace  of  the  original 
cartilage  can  be  present  in  the  femur  of  the  adult.  Its  purpose  is  indeed 
purely  temporary;  and,  after  its  calcification,  it  is  gradually  and  entirely 
re-absorbed  as  will  be  presently  explained. 


FIG.  61.  FIG.  52. 

FIG.  51.— From  a  transverse  section  through  part  of  foetal  jaw  near  the  extreme  periosteum, 
in  the  state  of  spongy  bone,  p,  fibrous  layer  of  periosteum :  6,  osteogenetic  layer  of  periosteum; 
o,  csteoblasts:  r.  osseous  substance,  containing  many  bone  corpuscles.  X  300.  'a^r^vi  \ 

FIG.  52.— Ossifying  cartilage  showing  loops  of  blood-vessels. 


wnror  ui    ucnusieiuii, 
(Schofield.) 


The  cartilaginous  rod  which  forms  the  foetal  femur  is  sheathed  in  a 
membrane  termed  the  perichondrium,  which  so  far  resembles  the  perios- 
teum described  above,  that  it  consists  of  two  layers,  in  the  deeper  one  of 
which  spheroidal  cells  predominate  and  blood-vessels  abound,  while  the 
outer  layer  consists  mainly  of  fusiform  cells  which  are  in  the  mature 
.tissue  gradually  transformed  into  fibres.  Thus,  the  differences  between 
VOL.  I.— 4. 


50 


HAND-BOOK    OF    PHYSIOLOGY. 


the  foetal  perichondrium  and  the  periosteum  of  the  adult  are  such  as 
usually  exist  between  the  embryonic  and  mature  forms  of  connective- 
tissue. 

Between  the  hyaline  cartilage  of  which  the  foetal  femur  consists  and 
the  bony  tissue  forming  the  adult  femur,  two  intermediate  stages  exist — 
Tiz.,  calcined  cartilage,  and  embryonic  spongy  bone.  These  tissues, 
•which,  successively  occupy  the  place  of  the  foetal  cartilage,  are  in  suc- 
cession entirely  re-absorbed,  and  their  place  taken  by  true  bone. 

The  process  by  which  the  cartilaginous  is  transformed  into  the  bony 


FIG.  53. 


FIG.  54. 


FIG.  53.  —  Longitudinal  section  of  ossifying  cartilage  from  the  humerus  of  a  foetal  sheep.  Calci- 
fied trabeculae  are  seen  extending  between  the  columns  of  cartilage  cells,  c,  cartilage  cells.  X  140. 
(Sharpey.) 

FIG.  54.  —  Transverse  section  of  a  portion  of  a  metacarpal  bone  of  a  foetus,  showing  —  1,  fibrous 
layer  of  periosteum;  2,  osteogenetic  layer  of  ditto;  3,  periosteal  bone;  4,  cartilage  with  matrix  gradu- 
ally becoming  calcified,  as  at  5,  with  cells  in  primary  areolae;  beyond  5  the  calcified  matrix  is  being 
entirely  replaced  by  spongy  bone.  X  300.  (V.  D.  Harris.) 

femur  may  be  divided  for  the  sake  of  clearness  into  the  following  six 
stages: 

Stage  I.  —  Vascularization  of  the  Cartilage.  —  Processes  from 
the  osteogenetic  or  cellular  layer  of  the  perichondrium  containing  blood- 
vessels grow  into  the  substance  of  the  cartilage  much  as  ivy  insinuates  it- 
self into  the  cracks  and  crevices  of  a  wall.  Thus  the  substance  of  the  car- 
tilage, which  previously  contained  no  vessels,  is  traversed  by  a  number  of 


STRUCTURE    OF    THE    ELEMENTARY   TISSUES. 


51 


"branched  anastomosing  channels  formed  by  the  enlargement  and  coales- 
cence of  the  spaces  in  which  the  cartilage-cells  lie,  and  containing  loops 
of  blood-vessels  (Fig.  52)  and  spheroidal-cells  which  will  become  osteo- 
blasts. 

Stage  2.— Calcification  of  Cartilaginous  Matrix. — Lime-salts 
are  next  deposited  in  the  form  of  fine  granules  in  the  hyaline  matrix  of 
the  cartilage,  which  thus  becomes  gradually  transformed  into  a  number 
of  calcified  trabeculae  (Fig.  54, B),  forming  alveolar  spaces  (primary  areolce) 
containing  cartilage  cells.  By  the  absorption  of  some  of  the  trabeculaa 
larger  spaces  arise,  which  contain  cartilage-cells  for  a  very  short  time 
only,  their  places  being  taken  by  the  so-called  osteogenetic  layer  of  the 
perichondrium  (before  referred  to  in  Stage  1)  which  constitutes  the  pri- 
mary marrow.  The  cartilage-cells,  gradually  enlarging,  become  more 
transparent  and  finally  undergo  disintegration. 

Stage  3.— Substitution  of  Embryonic  Spongy  Bone  for  Car- 
tilage.— The  cells  of  the  primary  marrow  arrange  themselves  as  a  con- 
tinuous layer  like  epithelium  on  the 
calcified  trabeculas  and  deposit  a  layer 
of  bone,  which  ensheathes  the  calcified 
trabeculae:  these  calcified  trabeculae, 
encased  in  their  sheaths  of  young  bone, 
become  gradually  absorbed,  so  that 
finally  we  have  trabeculae  composed  en- 
tirely of  spongy  bone,  all  trace  of  the 
original  calcified  cartilage  having  dis- 
appeared. It  is  probable  that  the  large 
multinucleated  giant-cells  termed  "os- 
teoclasts"  by  Kolliker,  which  are  de- 
rived from  the  osteoblasts  by  the  mul- 
tiplication of  their  nuclei,  are  the 
agents  by  which  the  absorption  of  cal- 
cified cartilage,  and  subsequently  of 
embryonic  spongy  bone,  is  carried  on 
(Fig.  55,  G).  At  any  rate  they  are 
almost  always  found  wherever  absorp- 
tion is  in  progress. 

Stages  2  and  3  are  precisely  similar  to  what  goes  on  in  the  growing 
shaft  of  a  bone  which  is  increasing  in  length  by  the  advance  of  the  pro- 
cess of  ossification  into  the  intermediary  cartilage  between  the  diaphysis 
and  epiphysis.  In  this  case  the  cartilage-cells  become  flattened  and, 
multiplying  by  division,  are  grouped  into  regular  columns  at  right  angles 
to  the  plane  of  calcification,  while  the  process  of  calcification  extends 
into  the  hyaline  matrix  between  them  (Figs.  52  and  53). 

Stage  4.— Substitution  of  Periosteal  Bone  for  the  Primary 


FIG.  55.— A  small  isolated  mass  of  bone  next 
the  periosteum  of  the  lower  jaw  of  human 
foetus,  a,  osteogenetic  layer  of  periosteum. 
G,  multinuclear  giant  cells,  the  one  on  the  left 
acting  here  probably  like  an  osteoclast.  Above 
c,  the  osteoblasts  are  seen  to  become  sur- 
rounded by  an  osseous  matrix.  (Klein  and 
Noble  Smith.) 


52 


HAND-BOOK    OF    PHYSIOLOGY. 


Embryonic  Spongy  Bone. — The  embryonic  spongy  bone,  formed  as 
above  described,  is  simply  a  temporary  tissue  occupying  the  place  of  the 
foetal  rod  of  cartilage,  once  representing  the  femur;  and  the  stages  1,  2, 
and  3  show  the  successive  changes  which  occur  at  the  centre  of  the  shaft. 
Periosteal  bone  is  now  deposited  in  successive  layers  beneath  the  perios- 
teum, i.e.,  at  the  circumference  of  the  shaft,  exactly  as  described  in  the 


FIG.  56.— Transverse  section  through  the  tibia  of  a  fostal  kitten  semi-diagrammatic.  X  60.  P, 
Periosteum.  O,  osteogenetic  layer  of  the  periosteum,  showing  the  osteoblasts  arranged  side  by  side, 
represented  as  pear-shaped  black  dots  oh  the  surface  of  the  newly-formed  bone.  B,  the  periostea! 
bone  deposited  in  successive  layers  beneath  the  periosteum  and  ensheathing  E,  the  spongy  endochon- 
dral  bone;  represented  as  more  deeply  shaded.  Within  the  trabeculae  of  endochonclral  spongy  bone 
are  seen  the  remains  of  the  calcified  cartilage  trabeculae  represented  as  dark  wavy  lines.  C,  the  me- 
dulla, with  V,  V,  veins.  In  the  lower  half  of  the  figure  the  endochondral  spongy  bone  has  been  com- 
pletely absorbed.  (Klein  and  Noble  Smith.) 

section  on  "ossification  in  membrane,"  and  thus  a  casing  of  periosteal 
bone  is  formed  around  the  embryonic  endochondral  spongy  bone:  this 
casing  is  thickest  at  the  centre,  where  it  is  first  formed,  and  thins  out 
toward  each  end  of  the  shaft.  The  embryonic  spongy  bone  is  absorbed, 
its  trabeculae  becoming  gradually  thinned  and  its  meshes  enlarging,  and 
finally  coalescing  into  one  great  cavity— the  medullary  cavity  of  the-  shaft. 
Stage  5.— Absorption  of  the  Inner  Layers  of  the  Periosteal 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


53 


Bone. — The  absorption  of  the  endochondral  spongy  bone  is  now  complete, 
and  the  medullary  cavity  is  bounded  by  periosteal  bone:  the  inner  layers 
of  this  periosteal  bone  are  next  absorbed,  and  the  medullary  cavity  is 
thereby  enlarged,  while  the  deposition  of  bone  beneath  the  periosteum 
continues  as  before.  The  first-formed  periosteal  bone  is  spongy  in  char- 
acter. 

Stage  6. — Formation  of  Compact  Bone. — The  transformation 
of  spongy  periosteal  bone  into  compact  bone  is  effected  in  a  manner 
exactly  similar  to  that  which  has  been  described  in  connection  with  ossi- 
fication in  membrane  (p.  47).  The  irregularities  in  the  walls  of  the 
areolae  in  the  spongy  bone  are 
absorbed,  while  the  osteoblasts 
which  line  them  are  developed 
in  concentric  layers,  each  layer 
in  turn  becoming  ossified  till  the 
comparatively  large  space  in  the 
centre  is  reduced  to  a  well- 
iormed  Haversian  canal  (Fig. 
57).  When  once  formed,  bony 
tissue  grows  to  some  extent  in- 
terstitially,  as  is  evidenced  by 
the  fact  that  the  lacunae  are 
rather  further  apart  in  fully- 
formed  than  in  young  bone. 

From  the  foregoing  descrip- 
tion of  the  development  of  bone, 
it  will  be  seen  that  the  common 
terms  "ossification  in  cartilage" 
and  "ossification  in  membrane" 
are  apt  to  mislead,  since  they 
seem  to  imply  two  processes  radi- 
cally distinct.  The  process  of 
ossification,  however,  is  in  all 
cases  one  and  the  same,  all  true  bony  tissue  being  formed  from  membrane 
(perichondrium  or  periosteum);  but  in  the  development  of  such  a  bone 
as  the  femur,  which  may  be  taken  as- the  type  of  so-called  "ossification  in 
cartilage,"  lime-salts  are  deposited  in  the  cartilage,  and  this  calcified  car- 
tilage is  gradually  and  entirely  re-absorbed,  being  ultimately  replaced  by 
bone  formed  from  the  periosteum,  till  in  the  adult  structure  nothing  but 
true  bone  is  left.  Thus,  in  the  process  of  "ossification  in  cartilage,"  cal- 
cification of  the  cartilaginous  matrix  precedes  the  real  formation  of  bone. 
We  must,  therefore,  clearly  distinguish  between  calcification  and  ossifica- 
tion. The  former  is  simply  the  infiltration  of  an  animal  tissue  with 
lime-salts,  and  is,  therefore,  a  change  of  chemical  composition  rather 


FIG.  57.— Transverse  section  of  femur  of  a  human 
embryo  about  eleven  weeks  old.  a,  rudimentary  Ha- 
versian canal  in  cross  section ;  6,  in  longitudinal  section ; 
c,  osteoblasts ;  ei,  newly  formed  osseous  substance  of  a 
lighter  color ;  e,  that  of  greater  age ;  /,  lacunae  with  their 
cells;  g,  a  cell  still  united  to  an  osteoblast.  (Frey.) 


54 


HAND-BOOK    OF    PHYSIOLOGY. 


than  of  structure;  while  ossification  is  the  formation  of  true  bone — a 
tissue  more  complex  and  more  highly  organized  than  that  from  which  it 
is  derived. 

Centres  of  Ossification. — In  all  bones  ossification  commences  at 
one  or  more  points,  termed  "centres  of  ossification."  The  long  bones, 
e.g.,  femur,  humerus,  etc.,  have  at  least  three  such  points — one  for  the 
ossification  of  the  shaft  or  diaphysis,  and  one  for  each  articular  extremity 
or  epiphysis.  Besides  these  three  primary  centres  which  are  always  pres- 
ent in  long  bones,  various  secondary  centres  may  be  superadded  for  the 
ossification  of  different  processes. 

Growth  of  Bone. — Bones  increase  in  length  by  the  advance  of  the 
process  of  ossification  into  the  cartilage  intermediate  between  the  dia- 
physis and  epiphysis.  The  increase  in  length  indeed  is  due  entirely  to 


FIG.  58.— A.  Longitudinal  section  of  a  human  molar  tooth;  c,  cement;  cZ,  dentine;  e,  enamel:  VT 
pulp  cavity.    (Owen.) 

B.  Transverse  section.    The  letters  indicate  the  same  as  in  A. 

growth  at  the  two  ends  of  the  shaft.  This  is  proved  by  inserting  two- 
pins  into  the  shaft  of  a  growing  bone:  after  some  time  their  distance 
apart  will  be  found  to  be  unaltered  though  the  bone  has  gradually  in- 
creased in  length,  the  growth  having  taken  place  beyond  and  not  be- 
tween them.  If  now  one  pin  be  placed  in  the  shaft,  and  the  other  in  the 
epiphysis,  of  a  growing  bone,  their  distance  apart  will  increase  as  the  bone 
grows  in  length. 

Thus  it  is  that  if  the  epiphyses  with  the  intermediate  cartilage  be  re- 
moved from  a  young  bone,  growth  in  length  is  no  longer  possible;  while  the 
natural  termination  of  growth  of  a  bone  in  length  takes  place  when  the 
epiphyses  become  united  in  bony  continuity  with  the  shaft. 

Increase  in  thickness  in  the  shaft  of  a  long  bone,  occurs  by  the  depo- 
sition of  successive  layers  beneath  the  periosteum. 

If  a  thin  metal  plate  be  inserted  beneath  the  periosteum  of  a  growing 
bone,  it  will  soon  be  covered  by  osseous  deposit,  but  if  it  be  put  between  the 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


55 


fibrous  and  osteogenetic  layers,  it  will  never  become  enveloped  in  bone, 
for  all  the  bone  is  formed  beneath  the  latter. 

Other  varieties  of  connective  tissue  may  become  ossified,  e.g.,  the 
tendons  in  some  birds. 

Functions  of  Bones.— Bones  form  the  framework  of  the  body;  for 
this  they  are  fitted  by  their  hardness  and  solidity  together  with  their  com- 
parative lightness;  they  serve  both  to  protect  internal  organs  in  the  trunk 
and  skull,  and  as  levers  worked  by  muscles 
in  the  limbs;  notwithstanding  their  hard-  z- 

ness  they  possess  a  considerable  degree  of 
elasticity,  which  often  saves  them  from 
fractures. 

TEETH. 

The  principal  part  of  a  tooth,  viz.,  den- 
tine, is  called  by  some  a  connective  tissue, 
and  on  this  account  the  structure  of  the 
teeth  is  considered  here. 

A  tooth  is  generally  described  as  pos- 
sessing a  crown,  neck,  and  fang  or  fangs. 

The  crown  js  the  portion  which  pro- 
jects beyond  the  level  of  the  gum.  The 
neck  is  that  constricted  portion  just  below 
the  crown  which  is  embraced  by  the  free 
edges  of  the  gum,  and  the  fang  includes  all 
below  this. 

On  making  a  longitudinal  section 
through  the  centre  of  a  tooth  (Figs.  58, 
59),  it  is  found  to  be  principally  composed 
of  a  hard  matter,  dentine  or  ivory;  while 
in  the  centre  this  dentine  is  hollowed  out 
into  a  cavity  resembling  in  general  shape 
the  outline  of  the  tooth,  and  called  the 
pulp  cavity,  from  its  containing  a  very 
mass,  composed  of  connective-tissue,  blood-vessels,  and  nerves,  which  is 
called  the  tooth-pulp. 

The  blood-vessels  and  nerves  enter  the  pulp  through  a  small  opening 
at  the  extremity  of  the  fang. 

Capping  that  part  of  the  dentine  which  projects  beyond  the  level  of 
the  gum,  is  a  layer  of  very  hard  calcareous  matter,  the  enamel;  while 
sheathing  the  portion  of  dentine  which  is  beneath  the  level  of  the  gum, 
is  a  layer  of  true  bone,  called  the  cement  or  crusta  petrosa. 


FIG.  59. — Premolar  tooth  of  cat  in  situ. 
Vertical  section.  1 .  Enamel  with  decus- 
sating and  parallel  striae.  2.  Dentine  with 
Schreger's  lines.  3.  Cement.  4.  Perios- 
teum of  alveolus.  5.  Inferior  maxillary 
bone  showing  canal  for  the  inferior 
dental  nerve  and  vessels  which  appears 
nearly  circular  in  transverse  section. 
(Waldeyer.) 

vascular  and   sensitive   little 


56  HAND-BOOK    OF    PHYSIOLOGY. 

At  the  neck  of  the  tooth,  where  the  enamel  and  cement  come  into 
contact,  each  is  reduced  to  an  exceedingly  thin  layer.  The  covering  of 
enamel  becomes  thicker  as  we  approach  the  crown,  and  the  cement  as  we 
approach  the  lower  end  or  apex  of  the  fang. 

L— 


Chemical  composition. — Dentine  or  ivory  in  chemical  composition 
closely  resembles  bone.  It  contains,  however,  rather  less  animal  matter; 
the  proportion  in  a  hundred  parts  being  about  twenty-eight  animal  to 
seventy-two  of  earthy.  The  former,  like  the  animal  matter  of  bone,  may 
be  resolved  into  gelatin  by  boiling.  The  earthy  matter  is  made  up  chiefly 
of  calcium  phosphate,  with  a  small  portion  of  the  carbonate,  and  traces 
of  calcium  fluoride  and  magnesium  phosphate. 

Structure. — Under  the  microscope  dentine  is  seen  to  be  finely  chan- 
neled by  a  multitude  of  delicate  tubes,  which,  by  their  inner  ends,  com- 


FIG.  60. — Section  of  a  portion  of  the  dentine  and  cement  from  the  middle  of  the  root  of  an  incisor 
tooth,  a,  dental  tubuli  ramifying  and  terminating,  some  of  them  in  the  interglobular  spaces  b  and  c, 
which  somewhat  resemble  bone  lacunae;  d,  inner  layer  of  the  cement  with  numerous  closely  set 
canaliculi;  e,  outer  layer  of  cement;/,  lacunae;  g,  canaliculi.  x  350.  (Kolliker.) 

municate  with  the  pulp-cavity,  and  by  their  outer  extremities  come  into 
contact  with  the  under  part  of  the  enamel  and  cement  and  sometimes 
even  penetrate  them  for  a  greater  or  less  distance  (Fig.  60). 

In  their  course  from  the  pulp-cavity  to  the  surface  of  the  dentine,  the 
minute  tubes  form  gentle  and  nearly  parallel  curves  and  divide  and  sub- 
divide dichotomously,  but  without  much  lessening  of  their  calibre  until 
they  are  approaching  their  peripheral  termination. 

From  their  sides  proceed  other  exceedingly  minute  secondary  canals, 
which  extend  into  the  dentine  between  the  tubules,  and  anastomose  with 
each  other.  The  tubules  of  the  dentine,  the  average  diameter  of  which 
at  their  inner  and  larger  extremity  is  T3V<r  °f  an  inch*  contain  fine  pro- 
longations from  the  tooth-pulp,  which  give  the  dentine  a  certain  faint 
sensitiveness  under  ordinary  circumstances,  and,  without  doubt,  have  to 
do  also  with  its  nutrition.  These  prolongations  from  the  tooth-pulp  are 
really  processes  of  the  dentine-cells  or  odontollasts  which  are  branched  cells 
lining  the  pulp-cavity;  the  relation  of  these  processes  to  the  tubules  in 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


57 


which  they  lie  being  precisely  similar  to  that  of  the  processes  of  the  bone- 
corpuscles  to  the  canaliculi  of  bone.  The  outer  portion  of  the  dentine, 
underlying  both  the  cement  and  enamel,  forms  a  more  or  less  distinct 
layer  termed  tlie  granular  or  inter  globular  layer.  It  is  characterized  by 
the~  presence  of  a  number  of  minute  cell- like  cavities,  much  more  closely 
packed  than  the  lacunae  in  the  cement,  and  communicating  with  one 
another  and  with  the  ends  of  the  dentine-tubes  (Fig.  60),  and  containing 
cells  like  bone-corpuscles. 

II. — Enamel. 

Chemical  composition. — The  enamel,  which  is  by  far  the  hardest  por- 
tion of  a  tooth,  is  composed,  chemically,  of  the  same  elements  that  enter 


a\   1* 


FIG.  61. 


FIG.  02. 


FIG.  61.— Thin  section  of  the  enamel  and  a  part  of  the  dentine,  a,  cutieular  pellicle  of  the  enamel; 
ft,  enamel  fibres,  or  columns  with  fissures  between  them  and  cross  striae:  c,  larger  cavities  in  the 
enamel,  communicating  with  the  extremities  of  some  of  the  tubuli  (d).  X  350.  (Kolliker.) 

FIG.  6-2.— Enamel  fibres.  A,  fragments  and  single  fibres  of  the  enamel,  isolated  by  the  action  of 
hydrochloric  acid.  B.  surface  of  a  small  fragment  of  enamel,  showing  the  hexagonal  ends  of  the 
fibres.  X350.  (Kolliker.) 

into  the  composition  of  dentine  and  bone.  Its  animal  matter,  however, 
amounts  only  to  about  %  or  3  per  cent.  It  contains  a  larger  proportion  of 
inorganic  matter  and  is  harder  than  any  other  tissue  in  the  body. 

Structure. — Examined  under  the  microscope,  enamel  is  found  com- 
posed of  fine  hexagonal  fibres  (Figs.  61,  62)  -rT5V?r  °f  an  incn  *n  diameter, 


58 


HAND-BOOK    OF    PHYSIOLOGY. 


which  are  set  on  end  on  the  surface  of  the  dentine,  and  fit  into  corre- 
sponding depressions  in  the  same. 

They  radiate  in  such  a  manner  from  the  dentine  that  at  the  top  of  the 
tooth  they  are  more  or  less  vertical,  while  toward  the  sides  they  tend  to 
the  horizontal  direction.  Like  the  dentine  tubules,  they  are  not  straight, 
but  disposed  in  wavy  and  parallel  curves.  The  fibres  are  marked  by 

transverse  lines,  and  are  mostly 
solid,  but  some  of  them  contain  a 
very  minute  canal. 

The  enamel-prisms  are  con- 
nected together  by  a  very  minute 
quantity  of  hyaline  cement-sub- 
stance. In  the  deeper  part  of  the 
enamel,  between  the  prisms,  are 
small  lacunce,  which  communicate 
with  the  "interglobular  spacdte" 
on  the  surface  of  the  dentine. 

The  enamel  itself  is  coated  on 
the  outside  by  a  very  thin  calci- 
fied membrane,  sometimes  termed 
the  cuticle  of  the  enamel. 


III. — Crusta  Petrosa. 

The  crusta  petrosa,  or  cement 
(Fig.  60,  c,  d],  is  composed  of  true 
bone,  and  in  it  are  lacunae  (/ )  and 
canaliculi  (g~)  which  sometimes 
communicate  with  the  outer  fine- 
ly branched  ends  of  the  dentine 
tubules.  Its  laminae  are  as  it  were 
bolted  together  by  perforating 
fibres  like  those  of  ordinary  bone, 
but  it  differs  in  possessing  Haver- 
sian  canals  only  in  the  thickest 
part. 

DEVELOPMENT  OF  TEETH. 


FIG.  63. — Section  of  the  upper  jaw  of  a  f  ratal  sheep. 
A.— 1,  common  enamel-germ  dipping  down  into  the 
mucous  membrane ;  2,  palatine  process  of  jaw.  B. — 
Section  similar  to  A,  but  passing  through  one  of  the 
special  enamel-germs  here  becoming  flask-shaped;  c, 
c',  epithelium  of  mouth;  /,  neck;  /',  body  of  special 
enamel-germ.  C. — A  later  stage ;  c,  outline  of  epithe- 
lium of  gum;  f,  neck  of  enamel-germ;  /',  enamel 
organ;  p,  papilla;  s,  dental  sac  forming 
enamel-germ  of  permanent  tooth.  (W 
Kolliker.)  Copied  from  Quain's  Anatomy. 


ng;  f  p,  the 
aldeyer  and 


Development  of  the  Teeth. — The 
first  step  in  the  development  of  the 
teeth  consists  in  a  downward  growth  (Fig.  63,  A,  1)  from  the  stratified 
epithelium  of  the  mucous  membrane  of  the  mouth,  now  thickened  in  the 
neighborhood  of  the  maxillae  which  are  in  the  course  of  formation.  This 
process  passes  downward  into  a  recess  (enamel  groove)  of  the  imperfectly 
developed  tissue  of  which  the  chief  part  of  the  jaw  consists.  The  down- 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


59 


ward  epithelial  growth  forms  the  primary  enamel  or  nan  or  enamel  germ, 
and  its  position  is  indicated  by  a  slight  groove  in  the  mucous  membrane 
of  the  jaw.  The  next  step  in  the  process  consists  in  the  elongation  down- 
ward of  the  enamel  groove  and  of  the  enamel  germ  and  the  inclination 
outward  of  the  deeper  part  (Fig.  63,  B,  /'),  which  is  now  inclined  at  an 
angle  with  the  upper  portion  or  neck  (/),  and  has  become  bulbous.  After 
this,  there  is  an  increased  development  at  certain  points  corresponding 
to  the  situations  of  the  future  milk  teeth,  and  the  enamel  germ,  or  com- 
mon enamel  germ,  as  it  may  be  called,  becomes  divided  at  its  deeper  por- 
tion, or  extended  by  further  growth,  into  a  number  of  special  enamel 
germs  corresponding  to  each  of  the  above-mentioned  milk  teeth,  and  con- 
nected to  the  common  germ  by  a  narrow  neck,  each  tooth  being  placed 
in  its  own  special  recess  in  the  embryonic  jaw  (Fig.  63,  B,//'). 

As  these  changes  proceed,  there  grows  up  from  the  underlying  tissue 
into  each  enamel  germ  (Fig.  63,  c,  p),  a  distinct  vascular  papilla  (dental 
papilla),  and  upon  it  the  enamel  germ 
becomes  moulded  and  presents  the  ap- 
pearance of  a  cap  of  two  layers  of  epi- 
thelium separated  by  an  interval  (Fig. 
63,  c,  /').  Whilst  part  of  the  sub- 
epithelial  tissue  is  elevated  to  form  the 
dental  papilla?,  the  part  which  bounds 
the  embryonic  teeth  forms  the  dental 
sacs  (Fig.  63,  c,  s);  and  the  rudiment 
of  the  jaw,  at  first  a  bony  gutter  in 
wrhich  the  teeth  germs  lie,  sends  up 
processes  forming  partitions  between 
the  teeth.  In  this  way  small  chambers 
are  produced  in  which  the  dental  sacs  are 
contained,  and  thus  the  sockets  of  the 
teeth  are  formed.  The  papilla,  which  is  really  part  of  the  dental  sac,  if 
one  thinks  of  this  as  the  whole  of  the  sub-epithelial  tissue  surrounding  the 
enamel  organ  and  interposed  between  the  enamel  germ  and  the  develop- 
ing bony  jaw,  is  composed  of  nucleated  cells  arranged  in  a  meshwork,  the 
outer  or  peripheral  part  being  covered  with  a  layer  of  columnar  nucleated 
cells  called  odontoUasts.  The  odontoblasts  form  the  dentine,  while  the 
remainder  of  the  papilla  forms  the  tooth-pulp.  The  method  of  the  for- 
mation of  the  dentine  from  the  odontoblasts  is  as  follows: — The  cells  elon- 
gate at  their  outer  part,  and  these  processes  are  directly  converted  into 
the  tubules  of  dentine  (Fig.  64).  The  continued  formation  of  dentine 
proceeds  by  the  elongation  of  the  odontoblasts,  and  their  subsequent  con- 
version by  a  process  of  calcification  into  dentine  tubules.  The  most 
recently  formed  tubules  are  not  immediately  calcified.  The  dentine  fibres 
contained  in  the  tubules  are  said  to  be  formed  from  processes  of  the 


FIG.  64.— Part  of  section  of  developing  tooth 
of  a  young  rat.  showing  the  mode  of  deposi- 
tion of  the  dentine.  Highly  magnified,  a, 
outer  layer  of  fully  formed  dentine :  ft.  uncal- 
cified  matrix  with  one  or  two  nodules  of  cal- 
careous matter  near  the  calcified  parts;  c, 
odontoblasts  sending  processes  into  the  den- 
tine; d,  pulp.  The  section  is  stained  in  car- 
mine, which  colors  the  uncalcified  matrix  but 
not  the  calcified  part.  (E.  A.  Schafer.) 


60 


HAND-BOOK    OF    PHYSIOLOGY. 


deeper  layer  of  odontoblasts,  which  are  wedged  in  between  the  cells  of 
the  superficial  layer  (Fig.  64)  which  form  the  tubules  only. 

Since  the  papillae  are  to  form  the  main  portion  of  each  tooth,  i.e.,  the 
dentine,  each  of  them  early  takes  the  shape  of  the  crown  of  the  tooth  it  is 
to  form.  As  the  dentine  increases  in  thickness,  the  papillae  diminish, 
and  at  last  when  the  tooth  is  cut,  only  a  small  amount  of  the  papilla 
remains  as  the  dental  pulp,  and  is  supplied  by  vessels  and  nerves  which 
enter  at  the  end  of  the  fang.  The  shape  of  the  crown  of  the  tooth  is 
taken  by  the  corresponding  papilla,  and  that  of  the  single  or  double  fang 

by  the  subsequent  constriction  be- 
low the  crown,  or  by  division  of  the 
lower  part  of  the  papilla. 

The  enamel  cap  is  found  later  on 
to  consist  (Fig.  65)  of  three  parts: 
(a)  an  inner  membrane,  composed 
of  a  layer  of  columnar  epithelium  in 
contact  with  the  dentine,  called  ena- 
mel cells,  and  outside  of  these  one  or 
more  layers  of  small  polyhedral  nu- 
cleated cells  (stratum  intermedium 
of  Hannover);  (V)  an  outer  mem- 
brane of  several  layers  of  epithelium; 
(c)  a  middle  membrane  formed  of  a 
matrix  of  non-vascular,  gelatinous 
tissue,  containing  a  hyaline  intersti- 
tial substance.  The  enamel  is  formed 
by  the  enamel  cells  of  the  inner 
membrane,  by  the  elongation  of 
their  distal  extremities,  and  the  di- 
rect conversion  of  these  processes 
into  enamel.  The  calcification  of 
the  enamel  processes  or  prisms  takes 
place  first  at  the  periphery,  the  cen- 
tre remaining  for  a  time  transparent.  The  cells  of  the  stratum  interme- 
dium are  used  for  the  regeneration  of  the  enamel  cells,  but  these  and 
the  middle  membrane  after  a  time  disappear.  The  cells  of  the  outer 
membrane  give  origin  to  the  cuticle  of  the  enamel. 

The  cement  or  crusta  petrosa  is  formed  from  the  tissue  of  the  tooth 
sac,  the  structure  and  function  of  which  are  identical  with  those  of  the 
osteogenetic  layer  of  the  periosteum. 

In  this  manner  the  first  set  of  teeth,  or  the  milk-teeth,  are  formed; 

and  each  tooth,  by  degrees  developing,  presses  at  length  on  the  wall  of  the 

sac  enclosing  it,  and,  causing  its  absorption,  is  cut,  to  use  a  familiar  phrase. 

The  temporary  or  milk-teeth  have  only  a  very  limited  term  of  existence. 


FIG.  65.— Vertical  transverse  section  of  the 
dental  sac,  pulp,  etc.,  of  a  kitten,  a,  dental 
papilla  or  pulp;  6,  the  cap  of  dentine  formed 
upon  the  summit;  c,  its  covering  of  enamel;  d, 
inner  layer  of  epithelium  of  the  enamel  organ;  e, 
gelatinous  tissue;  /,  outer  epithelial  layer  of  the 
enamel  organ ;  gr,  inner  layer,  and  h,  outer  layer 
of  dental  sac.  X  14.  (Thiersch.) 


STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  61 

This  is  due  to  the  growth  of  the  permanent  teeth,  which  push  their  way 
up  from  beneath,  absorbing  in  their  progress  the  whole  of  the  fang  of  each, 
milk-tooth  and  leaving  at  length  only  the  crown  as  a  mere  shell,  which, 
is  shed  to  make  way  for  the  eruption  of  the  permanent  teeth  (Fig.  66). 

The  temporary  teeth  are  ten  in  each  jaw,  namely,  four  incisors,  two 
canine,*,  and  four  molars,  and  are  replaced  by  ten  permanent  teeth,  each 
of  which  is  developed  in  a  way  almost  exactly  similar  to  the  manner  of 
development  already  described,  from  a  small  process  or  sac  set  by,  so  to 
speak,  from  the  enamel  germ  of  the  temporary  tooth  which  pfecedes  it, 
and  called  the  cavity  of  reserve. 

The  number  of  permanent  teeth  in  each  jaw  is,  however,  increased  to  six- 
teen, by  the  development  of  three  others  on  each  side  of  the  jaw  after  much 
the  same  fashion  as  that  by  which  the  milk-teeth  were  themselves  formed. 


FIG.  66.— Part  of  the  lower  jaw  of  a  child  of  three  or  four  years  old,  showing  the  relations  of  the 
temporary*  and  permanent  teeth.  The  specimen  contains  all  the  milk  teeth  of  the  right  side,  to- 
gether with  the  incisors  of  the  left;  the  inner  plate  of  the  jaw  has  been  removed,  so  as  to  expose  the 
sacs  of  all  the  permanent  teeth  of  the  right  side,  except  the  eighth  or  wisdom  tooth,  which  is  not  yet 
formed.  The  large  sac  near  the  ascending  ramus  of  the  jaw  is  that  of  the  first  permanent  molar,  and 
above  and  behind  it  is  the  commencing  rudiment  of  the  second  molar.  (Quain.) 

The  beginning  of  the  development  of  the  permanent  teeth  of  course 
takes  place  long  before  the  cutting  of  those  which  they  are  to  succeed. 
One  of  the  first  steps  in  the  development  of  a  milk-tooth  is  the  out- 
growth of  a  lateral  process  of  epithelial  cells  from  its  primitive  enamel 
organ  (Fig.  63,  c,  f  p}.  This  epithelial  outgrowth  ultimately  becomes 
the  enamel  organ  of  the  permanent  tooth,  and  is  indented  from  below  by 
a  primitive  dental  papilla,  precisely  as  described  above. 

The  following  formula  shows,  at  a  glance,  the  comparative  arrange- 
ment and  number  of  the  temporary  and  permanent  teeth: — 

Mo.  Ca.  In.  Ca.  Mo. 


( Upper     2 


Temporary  Teeth 4 -=20 

(Lower      21412     =10 

Mo.  Bi.  Ca.  In.  Ca.  Bi.  Mo. 


( Upper     3     2 


Permanent  Teeth 1 =32 

(  Lower     321412     3  =  16 


62 


HAND-BOOK    OF    PHYSIOLOGY. 


From  this  formula  it  will  be  seen  that  the  two  bicuspid  teeth  in  the 
adult  are  the  successors  of  the  two  molars  in  the  child.  They  differ  from 
them,  however,  in  some  respects,  the  temporary  molars  having  a  stronger 
likeness  to  the  permanent  than  to  their  immediate  descendants,  the  so- 
called  bicuspids. 

The  temporary  incisors  and  canines  differ  from  their  successors  but 
little  except  in  their  smaller  size. 

The  following  tables  show  the  average  times  of  eruption  of  the  Tem- 
porary arfd  Permanent  teeth.  In  both  cases,  the  eruption  of  any  given 
tooth  of  the  lower  jaw  precedes,  as  a  rule,  that  of  the  corresponding  tooth 
of  the  upper. 

Temporary  or  Milk  Teeth. 
The  figures  indicate  in  months  the  age  at  which  eacti  tooth  appears. 

Molars.  Canines.  Incisors.  Canines.  Molars. 


18       12    24 


Permanent  Teeth. 

The  age  at  which  each  tooth  is  cut  is  indicated  in  this  table  in  years. 
Molars.        Bicuspid.     Canines.      Incisors.      Canines.      Bicuspid.       Molars. 


17     12 
to  fto  6 
25     13 

1<J    9 

11  to  12 

8778 

11  to  12 

9     10 

12     17 
6  to    to 
13     25 

The  times  of  eruption  put  down  in  the  above  tables  are  only  approxi- 
mate: the  limits  of  variation  being  tolerably  wide.  Some  children  may 
cut  their  first  teeth  before  the  age  of  six  months,  and  others  not  till  nearly 
the  twelfth  month.  In  nearly  all  cases  the  two  central  incisors  of  the 
lower  jaw  are  cut  first;  these  being  succeeded  after  a  short  interval  by  the 
four  incisors  of  the  upper  jaw,  next  follow  the  lateral  incisors  of  the  lower 
jaw,  and  so  on  as  indicated  in  the  table  till  the  completion  of  the  milk 
dentition  at  about  the  age  of  two  years. 

The  milk-teeth  usually  come  through  in  batches,  each  period  of  erup- 
tion being  succeeded  by  one  of  quiescence  lasting  sometimes  several 
months.  The  milk-teeth  are  in  use  from  the  age  of  two  up  to  five  and  a 
half  years:  at  about  this  age  the  first  permanent  molars  (four  in  number) 
make  their  appearance  behind  the  milk-molars,  and  for  a  short  time  the 
child  has  four  permanent  and  twenty  temporary  teeth  in  position  at  once. 

It  is  worthy  of  note  that  from  the  age  of  five  years  to  the  shedding  of 
the  first  milk-tooth  the  child  has  no  fewer  than  forty-eight  teeth,  twenty 
milk-teeth  and  twenty-eight  calcified  germs  of  permanent  teeth  (all  in 
fact  except  the  four  wisdom  teeth). 


CHAPTER  IV. 

THE  BLOOD. 

THE  blood  of  man,  as  indeed  of  the  great  majority  of  vertebrate  ani- 
mals, is  a  more  or  less  viscid  fluid,  of  a  red  color.  The  exact  shade  of 
red  is  variable,  for  whereas  that  taken  from  the  arteries,  from  the  left 
side  of  the  heart  or  from  the  pulmonary  veins,  is  of  a  bright  scarlet  hue, 
that  obtained  from  the  systemic  veins,  from  the  right  side  of  the  heart, 
or  from  the  pulmonary  artery,  is  of  a  much  darker  color,  and  varies  from 
bluish-red  to  reddish-black.  To  the  naked  eye,  the  red  color  appears  to 
belong  to  the  whole  mass  of  blood,  but  on  examination  with  the  micro- 
scope it  is  found  that  this  is  not  the  case.  By  the  aid  of  this  instrument 
the  blood  is  shown  to  consist  in  reality  of  an  almost  colorless  fluid,  called 
Liquor  Sanguinis  or  Plasma,  in  which  are  suspended  numerous  minute 
rounded  masses  of  protoplasm,  called  Blood  Corpuscles.  The  corpuscles 
are,  for  the  most  part,  colored,  and  it  is  to  their  presence  that  the  red 
color  of  the  blood  is  due. 

Even  when  examined  in  very  thin  layers  blood  is  opaque,  on  account 
of  the  different  refractive  powers  possessed  by  its  two  constituents,  viz., 
the  plasma  and  the  corpuscles.  On  treatment  with  chloroform  and  other 
reagents,  however,  it  becomes  transparent,  and  assumes  a  lake  color,  in 
consequence  of  the  coloring  matter  of  the  corpuscles  having  been,  by 
these  means.,  discharged  into  the  plasma.  The  average  specific  gravity  of 
blood  at  60°  F.  (15°  C.)  is  1055,  the  extremes  consistent  with  health 
being  1045-1062.  The  reaction  of  blood  is  faintly  alkaline.  Its  temper- 
ature varies  within  narrow  limits,  the  average  being  100°  F.  (37 '8°  C.). 
The  blood  stream  is  slightly  warmed  by  passing  through  the  muscles, 
nerve  centres,  and  glands,  but  is  somewhat  cooled  on  traversing  the  capil- 
laries of  the  skin.  Recently  drawn  blood  has  a  distinct  odor,  which  in 
many  cases  is  characteristic  of  the  animal  from  which  it  has  been 
taken;  the  odor  may  be  further  developed  by  adding  to  blood  a  mixture 
of  equal  parts  of  sulphuric  acid  and  water. 

Quantity  of  the  Blood. — The  quantity  of  blood  in  any  animal  under 
normal  conditions  bears  a  pretty  constant  relation  to  the  body  weight. 
The  methods  employed  for  estimating  it  are  not  so  simple  as  might  at 
first  sight  be  thought.  For  example,  it  would  not  be  possible  to  get  any 
accurate  information  on  the  point  from  the  amount  obtained  by  rapidly 


64  HAND-BOOK    OF    PHYSIOLOGY. 

bleeding  an  animal  to  death,  for  then  an  indefinite  quantity  would  remain 
in  the  vessels,  as  well  as  in  the  tissues;  nor,  on  the  other  hand,  would  it 
be  possible  to  obtain  a  correct  estimate  by  less  rapid  bleeding,  as,  since  life 
would  be  more  prolonged,  time  would  be  allowed  for  the  passage  into  the 
blood  of  lymph  from  the  lymphatic  vessels  and  from  the  tissues.  In  the 
former  case,  therefore,  we  should  under-estimate,  and  in  the  latter  over- 
estimate the  total  amount  of  the  blood. 

Of  the  several  methods  which  have  been  employed,  the  most  accurate 
appears  to  be  the  following.  A  small  quantity  of  blood  is  taken  from  an 
animal  by  venesection;  it  is  defibrinated  and  measured,  and  used  to  make 
standard  solutions  of  blood.  The  animal  is  then  rapidly  bled  to  death, 
and  the  blood  which  escapes  is  collected.  The  blood-vessels  are  next 
washed  out  with  water  or  saline  solution  until  the  washings  are  no  longer 
colored,  and  these  are  added  to  the  previously  withdrawn  blood;  lastly 
the  whole  animal  is  finely  minced  with  water  or  saline  solution.  The 
fluid  obtained  from  the  mincings  is  carefully  filtered,  and  added  to  the 
diluted  blood  previously  obtained,  and  the  whole  is  measured.  Ths 
next  step  in  the  process  is  the  comparison  of  the  color  of  the  diluted  blood 
with  that  of  standard  solutions  of  blood  and  watsr  of  a  known  strength, 
until  it  is  discovered  to  what  standard  solution  the  diluted  blood  corre- 
sponds. As  the  amount  of  blood  in  the  corresponding  standard  solution 
is  known,  as  well  as  the  total  quantity  of  diluted  blood  obtained  from  the 
animal,  it  is  easy  to  calculate  the  absolute  amount  of  blood  which  the 
latter  contained,  and  to  this  is  added  the  small  amount  which  was  with- 
drawn to  make  the  standard  solutions.  This  gives  the  total  amount  of 
blood  which  the  animal  contained.  It  is  contrasted  with  the  weight  of 
the  animal,  previously  known.  The  result  of  many  experiments  shows 
that  the  quantity  of  blood  in  various  animals  averages  -fa  to  T^  of  the 
total  body  weight. 

An  estimate  of  the  quantity  in  man  which  corresponded  nearly  with 
the  above,  was  made  some  years  ago  from  the  following  data.  A  crim- 
inal was  weighed  before  and  after  decapitation;  the  difference  in  the 
weight  representing,  of  course,  the  quantity  of  blood  which  escaped. 
The  blood-vessels  of  the  head  and  trunk  were  then  washed  out  by  the  in- 
jection of  water,  until  the  fluid  which  escaped  had  only  a  pale  red  or  straw 
color.  This  fluid  was  then  also  weighed;  and  the  amount  of  blood  which 
it  represented  was  calculated  by  comparing  the  proportion  of  solid  matter 
contained  in  it  with  that  of  the  first  blood  which  escaped  on  decapitation. 
Two  experiments  of  this  kind  gave  precisely  similar  results.  (Weber  and 
Lehmann.) 

It  should  be  remembered,  however,  in  connection  with  these  estima- 
tions, that  the  quantity  of  the  blood  must  vary,  even  in  the  same  animal, 
very  considerably  with  the  amount  of  both  the  ingesta  and  egesta  of  the 
period  immediately  preceding  the  experiment;  and  it  has  been  found, 


THE    BLOOD. 


65 


indeed,  that  the  quantity  of  blood  obtainable  from  a  fasting  animal  barely 
exceeds  a  half  of  that  which  is  present  soon  after  a  full  meal. 

Coagulation  of  the  Blood. — One  of  the  most  characteristic  proper- 
ties which  the  blood  possesses  is  that  of  clotting  or  coagulating,  when 
removed  from  the  body.  This  phenomenon  may  be  observed  under  the 
most  favorable  conditions  in  blood  which  has  been  drawn  into  an  open 
vessel.  In  about  two  or  three  minutes,  at  the  ordinary  temperature  of 
the  air,  the  surface  of  the  fluid  is  seen  to  become  semi-solid  or  jelly-like; 
this  change  next  taking  place,  in  a  minute  or  two,  at  the  sides  of  the 
vessel  in  which  it  is  contained,  and  then  extending  throughout  the  entire 
mass. 

The  time  which  is  required  for  the  blood  to  become  solid  is  about  eight 
or  nine  minutes.  The  solid  mass  occupies  exactly  the  same  volume  as  the 
previously  liquid  blood,  and  adheres  so  closely  to  the  sides  of  the  contain- 


FIG.  67.— Reticulum  of  fibrin,  from  a  drop  of  human  blood,  after  treatment  with  rosanilin. 

(Ranvier.) 

ing  vessel  that  if  it  be  inverted  none  of  its  contents  escape.  The  solid 
mass  is  the  crassamentum  or  clot.  If  the  clot  be  watched  for  a  few  min- 
utes, drops  of  a  light  straw-colored  fluid,  the  serum,  may  be  seen  to  make 
their  appearance  on  the  surface,  and,  as  they  become  more  and  more  nu- 
merous, run  together,  forming  a  complete  superficial  stratum  above  the 
solid  clot.  At  the  same  time  the  fluid  begins  to  transude  at  the  sides  and 
at  the  under  surface  of  the  clot,  which  in  the  course  of  an  hour  or  two 
floats  in  the  liquid.  The  first  drops  of  serum  appear  on  the  surface  about 
eleven  or  twelve  minutes  after  the  blood  has  been  drawn;  and  the  fluid 
continues  to  transude  for  from  thirty-six  to  forty-eight  hours. 

The  clotting  of  blood  is  due  to  the  development  in  it  of  a  substance 
called  fibrin,  which  appears  as  a  meshwork  (Fig.  67)  of  fine  fibrils.  This 
meshwork  entangles  and  encloses  within  it  the  blood  corpuscles,  as  clot- 
ting takes  place  too  quickly  to  allow  them  to  sink  to  the  bottom  of  the 
plasma.  The  first  clot  formed,  therefore,  includes  the  whole  of  the  con- 
VOL.  I.— 5. 


00  HAND-BOOK    OF    PHYSIOLOGY. 

stituents  of  the  blood  in  an  apparently  solid  mass,  but  soon  the  fibrinous 
meshwork  begins  to  contract,  and  the  serum  which  does  not  belong  to  the 
clot  is  squeezed  out.  When  the  whole  of  the  serum  has  transuded,  the 
•clot  is  found  to  be  smaller,  but  firmer  and  harder,  as  it  is  now  made  up 
of  fibrin  and  blood  corpuscles  only.  It  will  be  noticed  that  coagulation 
rearranges  the  constituents  of  the  blood  according  to  the  following  scheme, 
liquid  blood  being  made  up  of  plasma  and  blood-corpuscles,  and  clotted 
blood  of  serum  and  clot. 

Liquid  Blood. 


Plasma  Corpuscles 

I 


Serum  Fibria 


I 
Clot 

I 


Clotted 


Blood 


Buffy  Coat. — Under  ordinary  circumstances  coagulation  occurs,  as 
we  have  mentioned  above,  before  the  red  corpuscles  have  had  time  to  sub- 
side; and  thus  from  their  being  entangled  in  the  meshes  of  the  fibrin,  the 
clot  is  of  a  deep  red  color  throughout,  somewhat  darker,  it  may  be,  at  the 
most  dependent  part,  from  accumulation  of  red  corpuscles,  but  not  to  any 
very  marked  degree.  When,  however,  coagulation  is  delayed  from  any 
cause,  as  when  blood  is  kept  at  a  temperature  of  32°  F.  (0°  C.),  or  when 
clotting  is  normally  a  slow  process,  as  in  the  case  of  horse's  blood,  or, 
lastly,  in  certain  diseased  conditions  of  the  blood  in  which  clotting  is 
naturally  delayed,  time  is  allowed  for  the  colored  corpuscles  to  sink  to  the 
bottom  of  the  fluid.  When  clotting  does  occur,  the  upper  layers  of  the 
blood,  being  free  of  colored  corpuscles  and  consisting  chiefly  of  fibrin, 
form  a  superficial  stratum  differing  in  appearance  from  the  rest  of  the 
clot,  in  that  it  is  of  a  grayish  yellow  color.  This  is  known  as  the  "buffy 
coat." 

Cupped  appearance  of  the  Clot. — When  the  buffy  coat  has  been 
produced  in  the  manner  just  described,  it  commonly  contracts  more  than 
the  rest  of  the  clot,  on  account  of  the  absence  of  colored  corpuscles  from 
its  meshes,  and  because  contraction  is  less  interfered  with  by  adhesion  to 
the  interior  of  the  containing  vessel  in  the  vertical  than  the  horizontal 
direction.  This  produces  a  cup-like  appearance  of  the  buffy  coat,  and  the 
clot  is  not  only  buffed  but  cupped  on  the  surface.  The  buffed  and  cupped 
appearance  of  the  clot  is  well  marked  in  certain  states  of  the  system, 
especially  in  inflammation,  where  the  fibrin-forming  constituents  are  in 
excess,  and  it  is  also  well  marked  in  chlorosis  where  the  corpuscles  are 
deficient  in  quantity. 


THE    BLOOD.  07 

Formation  of  Fibrin. — In  describing  the  coagulation  of  the  blood  in 
the  preceding  paragraphs,  it  was  stated  that  this  phenomenon  was  due  to 
the  development  in  the  clotting  blood  of  a  mesh  work  of  fibrin.  This  may 
be  demonstrated  by  taking  recently-drawn  blood,  and  whipping  it  with  a 
bundle  of  twigs;  the  fibrin  is  found  to  adhere  to  the  twigs  as  a  red  dish - 
white,  stringy  mass,  having  been  thus  obtained  from  the  fluid  nearly  free 
from  colored  corpuscles.  The  defibrinated  blood  no  longer  retains  the 
power  of  spontaneous  coagulability. 

The  fibrin  which  makes  its  appearance  in  the  blood  when  it  is  under- 
going coagulation  is  derived  chiefly,  if  not  entirely,  from  the  plasma  or 
liquor  sanguinis;  for  although  the  colorless  corpuscles  are  intimately  con- 
nected with  the  process  in  a  way  which  will  be  presently  explained,  the 
•colored  corpuscles  appear  to  take  no  active  part  in  it  whatever.  This 
may  be  shown  by  experimenting  with  plasma  free  from  colored  corpuscles. 
Such  plasma  may  be  procured  by  delaying  coagulation  in  blood,  by  keep- 
ing it  at  a  low  temperature,  32°  ~F.  (0°  C.),  until  the  colored  corpuscles 
which  are  of  higher  specific  gravity  than  the  other  constituents  of  blood, 
have  had  time  to  sink  to  the  bottom  of  the  containing  vessel,  and  to  leave 
mi  upper  stratum  of  colorless  plasma,  in  the  lower  layers  of  which  are 
many  colorless  corpuscles.  The  blood  of  the  horse  is  specially  suited  for 
the  purposes  of  this  experiment;  and  the  upper  stratum  of  colorless 
plasma  derived  from  it,  if  decanted  into  another  vessel  and  exposed  to  the 
ordinary  temperature  of  the  air,  will  coagulate  just  as  though  it  were  the 
entire  blood,  producing  a  clot  similar  in  all  respects  to  blood  clot,  except 
that  it  is  almost  colorless  from  the  absence  of  red  corpuscles.  If  some  of 
the  plasma  be  diluted  with  neutral  saline  solution,1  coagulation  is  de- 
layed, and  the  stages  of  the  gradual  formation  of  fibrin  may  be  more  con- 
veniently watched.  The  viscidity  which  precedes  the  complete  coagula- 
tion may  be  seen  to  be  due  to  fibrin  fibrils  developing  in  the  fluid — first 
of  all  at  the  circumference  of  the  containing  vessel,  and  gradually  extend- 
ing throughout  the  mass.  Again,  if  plasma  be  whipped  with  a  bundle  of 
twigs,  the  fibrin  may  be  obtained  as  a  solid,  stringy  mass,  just  in  the 
same  way  as  from  the  entire  blood,  and  the  resulting  fluid  no  longer 
retains  its  power  of  spontaneous  coagulability.  Evidently,  therefore, 
fibrin  is  derived  from  the  plasma  and  not  from  the  colored  corpuscles. 
In  these  experiments,  it  is  not  necessary  that  the  plasma  shall  have  been  ob- 
tained by  the  process  of  cooling  above  described,  as  plasma  obtained  in 
any  other  way,  e.g.,  by  allowing  blood  to  flow  direct  from  the  vessels  of 
an  animal  into  a  vessel  containing  a  third  or  a  fourth  of  the  bulk  of  the 
blood  of  a  saturated  solution  of  a  neutral  salt  (preferably  of  magnesium 
sulphate)  and  mixing  carefully,  will  answer  the  purpose,  and,  just  as  in 
the  other  case,  the  colored  corpuscles  will  subside,  leaving  the  clear  super- 

1  Xcutral  saline  solution  commonly  consists  of  a  '75  solution  of  common  salt 
(sodium  chloride)  in  water. 


68  HAND-BOOK    OF    PHYSIOLOGY. 

stratum  of  (salted)  plasma.  In  order  to  cause  this  plasma  to  coagulate, 
it  is  necessary  to  get  rid  of  the  salts  by  dialysis,  or  to  dilute  it  with  several 
times  its  bulk  of  water. 

The  antecedent  of  Fibrin. — If  plasma  be  saturated  with  solid 
magnesium  sulphate  or  sodium  chloride,  a  white,  sticky  precipitate-, 
called  plasmine,  is  thrown  down,  after  the  removal  of  which,  by  nitration, 
the  plasma  will  not  spontaneously  coagulate.  This  plasmine  is  soluble 
in  dilute  neutral  saline  solutions,  and  the  solution  of  it  speedily  coagu- 
lates, producing  a  clot  composed  of  fibrin.  From  this  we  see  that  blood 
plasma  contains  a  substance  without  which  it  cannot  coagulate,  and  a, 
solution  of  which  is  spontaneously  coagulable.  This  substance  is  very 
soluble  in  dilute  saline  solutions,  and  is  not,  therefore,  fibrin,  which  is 
insoluble  in  these  fluids.  We  are,  therefore,  led  to  the  belief  that  plas- 
mine produces  or  is  converted  into  fibrin,  when  clotting  of  fluids  contain- 
ing it  takes  place. 

Nature  of  Plasmine. — There  seems  distinct  evidence  that  plasmine 
is  a  compound  body  made  up  of  two  or  more  substances,  and  that  it  is 
not  mere  soluble  fibrin.  This  view  is  based  upon  the  following  observa- 
tions:— There  exists  in  all  the  serous  cavities  of  the  body  in  health,  e.g., 
the  pericardium,  the  peritoneum,  and  the  pleura,  a  certain  small  amount 
of  transparent  fluid,  generally  of  a  pale  straw  color,  which  in  diseased 
conditions  may  be  greatly  increased.  It  somewhat  resembles  serum  in 
appearance,  but  in  reality  differs  from  it,  and  is  probably  identical  with 
plasma.  This  serous  fluid  is  not,  as  a  rule,  spontaneously  coagulable,  but 
may  be  made  to  clot  on  the  addition  of  serum,  which  is  also  a  fluid  which 
has  no  tendency  of  itself  to  coagulate.  The  clot  produced  consists  of 
fibrin,  and  the  clotting  is  identical  with  the  clotting  of  plasma.  From 
the  serous  fluid  (that  from  the  inflamed  tunica  vaginalis  testis  or  hydrocele 
fluid  is  mostly  used)  we  may  obtain,  by  saturating  it  with  solid  mag- 
nesium sulphate  or  sodium  chloride,  a  white  viscid  substance  as  a  precipi- 
tate which  is  'called  fibrinogen,  which  may  be  separated  by  filtration,  and 
is  then  capable  of  being  dissolved  in  water,  as  a  certain  amount  of  the 
neutral  salt  is  entangled  with  the  precipitate  sufficient  to  produce  a  dilute 
saline  solution  in  which  it  is  soluble.  This  body  belongs  to  the  globulin 
class  of  proteid  substances.  Its  solution  has  no  tendency  to  clot  of  itself. 
Fibrinogen  may  also  be  obtained  as  a  viscid  precipitate  from  hydrocele 
fluid  by  diluting  it  with  water,  and  passing  a  brisk  stream  of  carbon 
dioxide  gas  through  the  solution.  Now  if  serum  be  added  to  a  solution 
of  fibrinogen,  the  mixture  clots. 

From  serum  may  be  obtained  another  globulin  very  similar  in  proper- 
ties to  fibrinogen,  if  it  be  subjected  to  treatment  similar  to  either  of  the 
two  methods  by  which  fibrinogen  is  obtained  from  hydrocele  fluid;  this 
substance  is  called  par  a  globulin,  and  it  may  be  separated  by  filtration  ar.d 
dissolved  in  a  dilute  saline  solution  in  a  manner  similar  to  fibrinogen. 


THE    BLOOD.  09 

If  the  solutions  of  fibrinogen  and  paraglobulin  be  mixed,  the  mixture 
cannot  be  distinguished  from  a  solution  of  plasmine,  and  like  that  solu- 
tion (in  a  great  majority  of  cases)  firmly  clots;  whereas  a  mixture  of  the 
hydrocele  fluid  and  serum,  from  which  they  have  been  respectively  taken, 
no  longer  does  so.  In  addition  to  this  evidence  of  the  compound  nature 
of  plasmine,  it  may  be  further  shown  that,  if  sufficient  care  be  taken, 
both  fibrinogen  and  paraglobulin  may  be  obtained  from  plasma:  fibrin- 
ogen, as  a  flaky  precipitate,  by  adding  carefully  1 3  per  cent,  of  crystalline 
sodium  chloride;  and  after  the  removal  of  fibrinogen  from  the  plasma  by 
filtration,  paraglobulin  may  be  afterward  precipitated,  on  the  further 
addition  of  the  same  salt  or  of  magnesium  sulphate  to  the  filtrate.  It  is 
evident,  therefore,  that  both  these  substances  must  be  thrown  down  to- 
gether when  plasma  is  saturated  with  sodium  chloride  or  magnesium  sul- 
phate, and  that  the  mixture  of  the  two  corresponds  with  plasmine. 

Presence  of  a  Fibrin  Ferment. — So  far  it  has  been  shown  that 
plasmine,  the  antecedent  of  fibrin  in  blood,  to  the  possession  of  which 
blood  owes  its  power  of  coagulating,  is  not  a  simple  body,  but  is  composed 
of  at  least  two  factors — viz.,  fibrinogen  and  paraglobulin;  there  is  reason 
for  believing  that  yet  another  body  is  associated  with  them  in  plasmine 
to  produce  coagulation;  this  is  what  is  known  under  the  name  of  fibrin 
ferment  (Schmidt).  It  was  at  one  time  thought  that  the  reason  why 
hydrocele  fluid  coagulated  when  serum  was  added  to  it  was  that  the  latter 
fluid  supplied  the  paraglobulin  which  the  former  lacked;  this,  however, 
is  not  the  case,  as  hydrocele  does  not  lack  this  body,  and  if  paraglobulin, 
obtained  from  serum  by  the  carbonic  acid  method,  be  added  to  it,  it  will 
not  coagulate,  neither  will  a  mixture  of  solutions  of  fibrinogen  and  para- 
globulin obtained  in  the  same  way.  But  if  paraglobulin,  obtained  by 
the  saturation  method,  be  added  to  hydrocele  fluid,  it  will  clot,  as  will 
also,  as  we  have  seen  above,  a  mixed  solution  of  fibrinogen  and  para- 
globulin, when  obtained  by  the  saturation  method.  From  this  it  is  evident 
that  in  plasmine  there  is  something  more  than  the  two  bodies  above  men- 
tioned, and,that  this  something  is  precipitated  with  the  paraglobulin  by 
the  saturation  method,  and  is  not  precipitated  by  the  carbonic  acid 
method.  The  following  experiments  show  that  it  is  of  the  nature  of  a 
ferment.  If  defibrinated  blood  or  serum  be  kept  in  a  stoppered  bottle 
with  its  own  bulk  of  alcohol  for  some  weeks,  all  the  proteid  matter  is  pre- 
cipitated in  a  coagulated  form;  if  the  precipitate  be  then  removed  by 
filtration,  dried  over  sulphuric  acid,  finely  powdered,  and  then  suspended 
in  water,  a  watery  extract  may  be  obtained  by  further  filtration,  contain- 
ing extremely  little,  if  any,  proteid  matter.  Yet  a  little  of  this  watery 
extract  will  determine  coagulation  in  fluids,  e.g.,  hydrocele  fluid  or 
diluted  plasma,  which  are  not  spontaneously  coagulable,  or  which  coagu- 
late slowly  and  with  difficulty.  It  will  also  cause  a  mixture  of  fibrinogen 
and  paraglobulin,  obtained  by  the  carbonic  acid  method,  to  clot.  This 


70  HAND-BOOK    OF    PHYSIOLOGY. 

watery  extract  appears  to  contain  the  body  which  is  precipitated  with  the 
paraglobulin  by  the  saturation  method.  Its  active  properties  are  entirely 
destroyed  by  boiling.  The  amount  of  the  extract  added  does  not  influ- 
ence the  amount  of  the  clot  formed,  but  only  the  rapidity  of  clotting,  and 
moreover  the  active  substance  contained  in  the  extract  evidently  does  not 
form  part  of  the  clot,  as  it  may  be  obtained  from  the  serum  after  blood 
has  clotted.  So  that  the  third  factor,  which  is  contained  in  the  aqueous- 
extract  of  blood,  belongs  to  that  class  of  bodies  which  promote  the  union 
of  other  bodies,  or  cause  changes  in  other  bodies,  without  themselves- 
entering  into  union  or  undergoing  change,  i.e.  ferments.  The  third  sub- 
stance has,  therefore,  received  the  name  fibrin  ferment.  This  ferment 
is  developed  in  blood  soon  after  it  has  been  shed,  and  its  amount  appears, 
to  increase  for  a  certain  time  afterward  (p.  74). 

The  part  played  by  Paraglobulin. — So  far  we  have  seen  that 
plasmine  is  a  body  composed  of  three  substances,  viz.,  fibrinogen,  para- 
globulin, and  fibrin  ferment.  The  question  presents  itself,  are  these 
three  bodies  actively  concerned  in  the  formation  of  fibrin?  Here  we 
come  to  a  point  about  which  two  distinct  opinions  prevail,  and  which  it 
will  be  necessary  to  mention.  Schmidt  holds  that  fibrin  is  produced  by 
the  interaction  of  the  two  proteid  bodies,  viz.,  fibrinogen  and  para- 
globulin, brought  about  by  the  presence  of  a  special  fibrin  ferment.  Also, 
that  when  coagulation  does  not  occur  in  serum,  which  contains  para- 
globulin and  the  fibrin  ferment,  the  non-coagulation  is  accounted  for  by 
lack  of  fibrinogen,  and  when  it  does  not  occur  in  fluids  which  contain 
fibrinogen,  it  is  due  to  the  absence  of  paraglobulin,  or  of  the  ferment,  or 
of  both.  It  will  be  seen  that,  according  to  this  view,  paraglobulin  has 
a  very  important  fibrino-plastic  property.  The  other  opinion,  held  by 
Hammersten,  is  that  paraglobulin  is  not  an  essential  in  coagulation,  or 
at  any  rate  does  not  take  an  active  part  in  the  process.  He  believes  that 
paraglobulin  possesses  the  property  in  common  with  many  other  bodies 
of  combining  with — or  decomposing,  and  so  rendering  inert — certain 
substances  which  have  the  power  of  preventing  the  formation,  or  precipi- 
tation of  fibrin,  this  power  of  preventing  coagulation  being  well  known 
to  belong  to  the  free  alkalies,  to  the  alkaline  carbonates,  and  to  certain 
salts;  and  he  looks  upon  fibrin  as  formed  from  fibrinogen,  which  is  either 
(1)  decomposed  into  that  substance  with  the  production  of  some  other 
substances;  or  (2)  bodily  converted  into  it  under  the  action  of  a  ferment,, 
which  is  frequently  precipitated  with  paraglobulin. 

Influence  of  Salts  on  Coagulation. — It  is  believed  that  the  pres- 
ence of  a  certain  but  small  amount  of  salts,  especially  of  sodhini  chloride, 
is  necessary  for  coagulation,  and  that  without  it,  clotting  cannot  take 
place. 

Sources  of  the  Fibrin  Generators.— It  has  been  previously  re- 
marked that  the  colorless  corpuscles  which  are  always  present  in  smaller 


THE    BLOOD. 


71 


or  greater  numbers  in  the  plasma,  even  when  this  has  been  freed  from 
colored  corpuscles,  have  an  important  share  in  the  production  of  the  clot. 
The  proofs  of  this  may  be  briefly  summarized  as  follows: — (1)  That  all 
strongly  coagulable  fluids  contain  colorless  corpuscles  almost  in  direct 
proportion  to  their  coagulability;  (2)  That  clots  formed  on  foreign  bodies, 
such  as  needles  inserted  into  the  interior  of  living  blood-vessels,  are  pre- 
ceded by  an  aggregation  of  colorless  corpuscles;  (3)  That  plasma  in 
which  the  colorless  corpuscles  happen  to  be  scanty,  clots  feebiy;  (4)  That 
if  horse's  blood  be  kept  in  the  cold,  so  that  the  corpuscles  subside,  it 
will  be  found  that  the  lowest  stratum,  containing  chiefly  colored  cor- 
puscles, will,  if  removed,  clot  feebly,  as  it  contains  little  of  the  fibrin 
faetors;  whereas  the  colorless  plasma,  especially  the  lower  layers  of  it  in 
which  the  colorless  corpuscles  are  most  numerous,  will  clot  well,  but  if 
filtered  in  the  cold  will  not  clot  so  well,  indicating  +hat  when  filtered 
nearly  free  from  colorless  corpuscles  even  the  plasma  does  not  contain  suffi- 
cient of  all  the  fibrin  factors  to  produce  thorough  coagulation;  (5)  In  a 
drop  of  coagulating  blood,  observed  under  the  miscroscope,  the  fibrin 
fibrils  are  seen  to  start  from  the  colorless  corpuscles. 

Although  the  intimate  connection  of  the  colorless  corpuscles  with  the 
process  of  coagulation  seems  indubitable,  for  the  reasons  just  given,  the 
exact  share  which  they  have  in  contributing  the  various  fibrin  factors 
remains  still  uncertain.  It  is  generally  believed  that  the  fibrin-ferment 
at  any  rate  is  contributed  by  them,  inasmuch  as  the  quantity  of  this  sub- 
stance obtainable  from  plasma  bears  a  direct  relation  to  the  numbers  of 
colorless  corpuscles  which  the  plasma  contains.  Many  believe  that  the 
fibrinogen  also  is  wholly  or  in  part  derived  from  them. 

Conditions  affecting  Coagulation. — The  coagulation  of  the  blood 
is  hastened  by  the  following  means: — 

1.  Moderate  warmth,— from  about  100°  to  120°  F.  (37-8—49°  C.). 

2.  Rest  is  favorable  to  the  coagulation  of  blood.    Blood,  of  which  the 
whole  mass  is  kept  in  uniform  motion,  as  when  a  closed  vessel  completely 
filled  with   it   is   constantly  moved,  coagulates  very  slowly  and   imper- 
fectly. 

3.  Contact  with  foreign  matter,  and  especially  multiplication  of 
the  points  of  contact.     Thus,  coagulated  fibrin  may  be  quickly  obtained 
from  liquid  blood  by  stirring  it  with  a  bundle  of  small  twigs;  and  even 
in  the  living  body  the  blood  will  coagulate  upon  rough  bodies  projecting 
into  the  vessels;  as,  for  example,  upon  threads  passed  through  them,  or 
upon  the  heart's  valves  roughened  by  inflammatory  deposits  or  calcareous 
accumulations. 

1.  The  free  access  of  air. — Coagulation  is  quicker  in  shallow  than 
in  tall  and  narrow  vessels. 


72  HAND-BOOK    OF    PHYSIOLOGY. 

5.  The  addition  of  less  than  twice  the  bulk  of  water. 

The  blood  last  drawn  is  said  to  coagulate  more  quickly  than  the  first. 
The  coagulation  of  the  blood  is  retarded,  suspended,  or  prevented 
by  the  following  means: — 

1.  Cold  retards  coagulation;  and  so  long  as  blood  is  kept  at  a  tem- 
perature, 32°  F.  (0°  C.),  it  will  not  coagulate  at  all.     Freezing  the  blood, 
of  course,  prevents  its  coagulation;  yet  it  will  coagulate,  though  not  firmly, 
if  thawed  after  being  frozen;  and  it  will  do  so,  even  after  it  has  been  frozen 
for  several  months.  A  higher  temperature  than  120°  F.  (49°  C. )  retards  coag- 
ulation, or,  by  coagulating  the  albumen  of  the  serum,  prevents  it  altogether. 

2.  The  addition  of  water  in  greater  proportion  than  twice  the 
bulk  of  the  blood.  • 

3.  Contact  with  living  tissues,  and  especially  with  the  interior 
of  a  living  blood-vessel. 

4.  The  addition  of  neutral  salts  in  the  proportion  of  2  or  3  per 
cent,  and  upward.     When  added  in  large  proportion  most  of  these  saline 
substances  prevent  coagulation  altogether.     Coagulation,  however,  ensues 
on  dilution  with  water.     The  time  during  which  blood  can  be  thus  pre- 
served in  a  liquid  state  and  coagulated  by  the  addition  of  water,  is  quite 
indefinite. 

5.  Imperfect  Aeration, — as  in  the  blood  of  those  who  die  by  as- 
phyxia. 

6.  In  inflammatory  states  of  the  system  the  blood  coagulates 
more  slowly  although  more  firmly. 

7.  Coagulation  is  retarded  by  exclusion  of  the  blood  from  the 
air,  as  by  pouring  oil  on  the  surface,  etc.     In  vacuo,  the  blood  coagulates 
quickly;  but  Lister  thinks  that  the  rapidity  of  the  process  is  due  to  the 
bubbling  which  ensues  from  the  escape  of  gas,  and  to  the  blood  being 
thus  brought  more  freely  into  contact  with  the  containing  vessel. 

8.  The  coagulation  of  the  blood  is  prevented  altogether  by  the  ad- 
dition of  strong  acids  and  caustic  alkalies. 

9.  It  has  been  believed,  and  chiefly  on  the  authority  of  Hunter,  that 
after  certain  modes  of  death  the  blood  does  not  coagulate; 
he  enumerates  the  death  by  lightning,  over-exertion  (as  in  animals  hunted 
to  death),  blows  on  the  stomach,  fits  of  anger.     He  says,  "I  have  seen 
instances  of  them  all."    Doubtless  he  had  done  so;  but  the  results  of  such 
events  are  not  constant.     The  blood  has  been  often  observed  coagulated 
in  the  bodies  of  animals  killed  by  lightning  or  an  electric  shock;  and 
Gulliver  has  published  instances  in  which  he  found  clots  in   the  hearts 
of  hares  and  stags  hunted  to  death,  and  of  cocks  killed  in  fighting. 

Cause  of  the  fluidity  of  the  blood  within  the  living  body.— 
Very  closely  connected  with  the  problem  of  the  coagulation  of  the  blood 
arises  the  question, — why  does  the  blood  remain  liquid  within  the  living 
body?  We  have  certain  pathological  and  experimental  facts,  apparently 


THE    BLOOD.  73 

opposed  to  one  another,  which  bear  upon  it,  and  these  may  be,  for  the 
sake  of  clearness,  classed  under  two  heads: — 

(1)  Blood  iv  ill  coagulate  within  the  living  body  under  certain  condi- 
tions,— for  example,  on  ligaturing  an  artery,  whereby  the  inner  and  mid- 
dle coats  are  generally  ruptured,  a  clot  will  form  within  it,  or  by  passing 
a  needle  through  the  coats  of  the  vessel  into  the  blood  stream  a  clot  will 
gradually  form  upon  it.     Other  foreign  bodies,  e.g.  wire,  thread,  etc., 
produce  the  same  effect.     It  is  a  well-known  fact  that  small  clots  are  apt 
to  form  upon  the  roughened  edges  of  the  valves  of  the  heart  when  the 
roughness  has  been  produced  by  inflammation,  as  in  endocarditis,  and  it 
is  also  equally  true  that  aneurisms  of  arteries  are  sometimes  spontaneously 
cured  by  the  deposition  within  them,  layer  by  layer,  of  fibrin  from  the 
blood  stream,  which  natural  cure  it  is  the  aim  of  the  physician  or  surgeon 
to  imitate. 

(2)  Blood  will  remain  liquid  under  certain  conditions  outside  the  body, 
without  the  addition  of  any  re-agent,  even  if  exposed  to  the  air  at  the 
ordinary  temperature.     It  is  well  known  that  blood  remains  fluid  in  the 
body  for  some  time  after  death,  and  it  is  only  after  rigor  mortis  has  oc- 
curred that  the  blood  is  found  clotted.     It  has  been  demonstrated  by 
Hewson,  and  also  by  Lister,  that  if  a  large  vein  in  the  horse  or  similar 
animal  be  ligatured  in  two  places  some  inches  apart,  and  after  some  time 
be  opened,  the  blood  contained  within  it  will  be  found  fluid,  and  that 
coagulation  will  occur  only  after  a  considerable  time.     But  this  is  not 
due  to  occlusion  from  the  air  simply.     Lister  further  showed  that  if  the 
vein  with  the  blood  contained  within  it  be  removed  from  the  body  and 
then  be  carefully  opened,  the  blood  might  be  poured  from  the  vein  into 
another  similarly  prepared,  as  from  one  test-tube  into  another,  thereby 
suffering  free  exposure  to  the  air,  without  coagulation  occurring  as  long 
as  the  vessels  retain  their  vitality.     If  the  endothelial  lining  of  the  vein, 
however,  be  injured,  the  blood  will  not  remain  liquid.     Again,  blood  will 
remain  liquid  for  days  in  the  heart  of  a  turtle,  which  continues  to  beat 
for  a  very  long  time  after  removal  from  the  body. 

Any  theory  which  aims  at  explaining  the  fluidity  under  the  usual 
conditions  of  the  blood  within  the  living  body  must  reconcile  the  above 
apparently  contradictory  facts,  and  must  at  the  same  time  be  made  to  in- 
clude all  the  other  known  facts  concerning  the  coagulation  of  the  blood. 
"We  may  therefore  dismiss  as  insufficient  the  following; — that  coagulation 
is  due  to  exposure  to  the  air  or  oxygen;  that  it  is  due  to  the  cessation  of 
the  circulatory  movement;  that  it  is  due  to  evolution  of  various  gases,  or 
to  the  loss  of  heat. 

Two  theories,  those  of  Lister  and  Briicke,  remain.  The  former  sup- 
poses that  the  blood  has  no  natural  tendency  to  clot,  but  that  its  coagula- 
tion out  of  the  body  is  due  to  the  action  of  foreign  matter  with  which  it 
happens  to  be  brought  into  contact,  and  in  the  body  to  conditions  of  the 


74  HAND-BOOK    OF    PHYSIOLOGY. 

tissues  which  cause  them  to  act  toward  it  like  foreign  matter.  The  lat- 
ter, on  the  other  hand,  supposes  that  there  is  a  natural  tendency  on  the 
part  of  the  blood  to  clot,  but  that  this  is  restrained  in  the  living  body 
by  some  inhibitory  power  resident  in  the  walls  of  the  containing  vessels. 

Support  was  once  thought  to  be  given  to  Briicke's  and  like  theories 
by  cases  of  injury,  in  which  blood  extravasated  in  the  living  body  has 
seemed  to  remain  uncoagulated  for  weeks,  or  even  months,  on  account  of 
its  contact  with  living  tissues.  But  the  supposed  facts  have  been  shown  to 
be  without  foundation.  The  blood-like  fluid  in  such  cases  is  not  uncoag- 
ulated blood,  but  a  mixture  of  serum  and  blood-corpuscles,  with  a  certain 
proportion  of  clot  in  various  stages  of  disintegration.  (Morrant  Baker.) 

As  the  blood  must  contain  the  substances  from  which  fibrin  is  formed, 
and  as  the  re-arrangement  of  these  substances  occurs  very  quickly  when- 
ever the  blood  is  shed,  so  that  it  is  somewhat  difficult  to  prevent  coagula- 
tion, it  seems  more  reasonable  to  hold  with  Briicke,  that  the  blood  has  a 
strong  tendency  to  clot,  rather  than  with  Lister,  that  it  has  no  special 
tendency  thereto. 

It  has  been  recently  suggested  that  the  reason  why  blood  does  not 
coagulate  in  the  living  vessels,  is  that  the  factors  which  we  have  seen  are 
necessary  for  the  formation  of  fibrin  are  not  in  the  exact  state  required 
for  its  production,  and  that  the  fibrin  ferment  is  not  formed  or  is  not,  at 
any  rate,  free  in  the  living  blood,  but  that  it  is  produced  (or  set  free)  at 
the  moment  of  coagulation  by  the  disintegration  of  the  colorless  corpuscles. 
This  supposition  is  certainly  plausible,  but  if  it  be  a  true  one,  it  must  be 
assumed  either  that  the  living  blood-vessels  exert  a  restraining  influence 
upon  the  disintegration  of  the  corpuscles  in  sufficient  numbers  to  form  a 
clot,  or  that  they  render  inert  any  small  amount  of  fibrin  ferment  which 
may  have  been  set  free  by  the  disintegration  of  a  few  corpuscles;  as  it  is 
certain  that  corpuscles  of  all  kinds  must  from  time  to  time  disintegrate 
in  the  blood  without  causing  it  to  clot;  and,  secondly,  that  shed  and 
defibrinated  blood  which  contains  blood  corpuscles,  broken  down  and  dis- 
integrated, will  not,  when  injected  into  the  vessels  of  an  animal,  produce 
clotting.  There  must  be  a  distinct  difference,  therefore,  if  only  in 
amount,  between  the  normal  disintegration  of  a  few  colorless  corpuscles  in 
the  living  uninjured  blood-vessels  and  the  abnormal  disintegration  of  a 
large  number  which  occurs  whenever  the  blood  is  shed  without  suitable 
precaution,  or  when  coagulation  is  unrestrained  by  the  neighborhood  of 
the  living  uninjured  blood-vessels. 

THE  BLOOD  COKPUSCLES  OK  BLOOD-CELLS. 

There  are  two  principal  forms  of  corpuscles,  the  red  and  the  white, 
or,  as  they  are  now  frequently  named,  the  colored  and  the  colorless. 
In  the  moist  state,  the  red  corpuscles  form  about  45  per  cent,  by  weight, 


THE    BLOOD 


75 


of  the  whole  mass  of  the  blood.     The  proportion  of  colorless  corpuscles 
is  only  as  1  to  500  or  600  of  the  colored. 

Red  or  Colored  Corpuscles. — Human  red  blood-corpuscles  are 
circular,  biconcave  disks  with  rounded  edges,  from  -3-^-5-  to  oVo  incn  i*1 
dia-metiT,  and  y^-o^-  inch  in  thickness,  becoming  flat  or  convex  on  addi- 
tion of  water.  When  viewed  singly,  they  appear  of  a  pale  yellowish  tinge; 
the  deep  red  color  which  they  give  to  the  blood  being  observable  in  them 
only  when  they  are  seen  en  masse.  They  are  composed  of  a  colorless, 
structureless,  and  transparent  filmy  framework  or  stroma,  infiltrated  in 
ill  parts  by  a  red  coloring  matter  termed  hemoglobin.  The  stroma  is 
tough  and  elastic,  so  that,  as  the  cells  circulate,  they  admit  of  elongation 
and  other  changes  of  form,  in  adaptation  to  the  vessels,  yet  recover  their 
natural  shape  as  soon  as  they  escape  from  compression.  The  term  cell, 
in  the  sense  of  a  bag  or  sac,  is  inapplicable  to  the  red  blood  corpus- 
cle; and  it  must  be  considered,  if  not 
solid  throughout,  yet  as  having  no  such 
variety  of  consistence  in  different  parts 
as  to  justify  the  notion  of  its  being  a 
membranous  sac  with  fluid  contents. 
The  stroma  exists  in  all  parts  of  its  sub- 
stance, and  the  coloring-matter  uni- 
formly pervades  this,  and  is  not  merely 
surrounded  by  and  mechanically  en- 
closed within  the  outer  wall  of  the 
corpuscle.  The  red  corpuscles  have 
no  nuclei,  although,  in  their  usual  state, 
the  unequal  refraction  of  transmitted  FIG  es.-Red  corpuscles  in  rouleaux  At 
light  gives  the  appearance  of  a  central  «,^  are  two  white  corpuscles. 

>t,  brighter  or  darker  than  the  border,  according  as  it  is  viewed  in  or 
mt  of  focus.  Their  specific  gravity  is  about  1088. 

Varieties. — The  red  corpuscles  are  not  all  alike,  some  being  rather 
larger,  paler,  and  less  regular  than  the  majority,  and  sometimes  flat  or 
slightly  convex,  with  a  shining  particle  apparent  like  a  nucleolus.  In 
almost  every  specimen  of  blood  may  be  also  observed  a  certain  number  of 
corpuscles  smaller  than  the  rest.  They  are  termed  m.icrocytes,  and  are 
probably  immature  corpuscles. 

A  peculiar  property  of  the  red  corpuscles,  exaggerated  in  inflammatory 
blood,  may  be  here  again  noticed,  i.e.,  their  great  tendency  to  adhere  to- 
gether in  rolls  or  columns,  like  piles  of  coins.  These  rolls  quickly  fasten 
together  by  their  ends,  and  cluster;  so  that,  when  the  blood  is  spread  out 
thinly  on  a  glass,  they  form  a  kind  of  irregular  network,  with  crowds  of 
corpuscles  at  the  several  points  corresponding  with  the  knots  of  the  net 
(Fig.  08).  Hence,  the  clot  formed  in  such  a  thin  layer  of  blood  looks 
mottled  with  blotches  of  pink  upon  a  white  ground,  and  in  a  larger  quan- 


76 


HAND-BOOK    OF    PHYSIOLOGY. 


tity  of  such  blood  help,  by  the  consequent  rapid  subsidence  of  the  cor- 
puscles, in  the  formation  of  the  buffy  coat  already  referred  to. 

This  tendency  on  the  part  of  the  red  corpuscles,  to  form  rouleaux,  is 
probably  only  a  physical  phenomenon,  comparable  to  the  collection  into 
somewhat  similar  rouleaux  of  discs  of  corks  when  they  are  partially  im- 
mersed in  water.  (Norris.) 

Mammals.      Birds.       Reptiles.  Amphibia.  Fish. 


FIG.  69.1 


1  The  above  illustration  is  somewhat  altered  from  a  drawing  by  Gulliver,  in  the 
Proceed.  Zool.  Society,  and  exhibits  the  typical  characters  of  the  red  blood-cells  in  the 
main  divisions  of  the  Vertebrata.  The  fractions  are  those  of  an  inch,  and  represent 
the  average  diameter.  .In  the  case  of  the  oval  cells,  only  the  long  diameter  is  here 
given.  It  is  remarkable,  that  although  the  size  of  the  red  blood-cells  varies  so  much 
in  the  different  classes  of  the  vertebrate  kingdom,  that  of  the  white  corpuscles  re- 
mains comparatively  uniform,  and  thus  they  are,  in  some  animals,  much  greater,  in 
others  much  less  than  the  red  corpuscles  existing  side  by  side  with  them. 


THE    BLOOD. 


77 


Action  of  Reagents. — Considerable  light  has  been  thrown  on  the 
physical  and  chemical  constitution  of  red  blood- cells  by  studying  the 
effects  produced  by  mechanical  means  and  by  various  reagents:  the  fol- 
lowing is  a  brief  summary  of  these  reactions: — 

Pressure. — If  the  red  blood-cells  of  a  frog  or  man  are  gently  squeezed, 
they  exhibit  a  wrinkling  of  the  surface,  which  clearly  indicates  that  there 
is  a  superficial  pellicle  partly  differentiated  from  the  softer  mass  within; 
airain,  if  a  needle  be  rapidly  drawn  across  a  drop  of  blood,  several  cor- 
puscles will  be  found  cut  in  two,  but  this  is  not  accompanied  by  any  es- 
cape of  cell  contents;  the  two  halves,  on  the  contrary,  assume  a  rounded 
form,  proving  clearly  that  the  corpuscles  are  not  mere  membranous  sacs 
with  fluid  contents  like  fat-cells. 

Fluids. —  Water. — When  water  is  added  gradually  to  frog's  blood,  the 
oval  disc-shaped  corpuscles  become  spherical,  and  gradually  discharge 
their  haemoglobin,  a  pale,  transparent  stroma  being  left  behind;  human 
red  blood-cells  change  from  a  discoidal  to  a  spheroidal  form,  and  dis- 
charge their  cell-contents,  becoming  quite  transparent  and  all  but  invisible. 

Saline  solution  (dilute)  produces  no  appreciable  effect  on  the  red 


FIG.  70. 

blood-cells  of  the  frog.  In  the  red  blood-cells  of  man  the  discoid  shape  is 
exchanged  for  a  spherical  one,  with  spinous  projections,  like  a  horse- 
chestnut  (Fig.  70).  Their  original  forms  can  be  at  once  restored  by  the 
use  of  carbonic  acid. 

Acetic  acid  (dilute)  causes  the  nucleus  of  the  red  blood  cells  in  the 
frog  to  become  more  clearly  defined;  if  the  action  is  prolonged,  the  nu- 
cleus becomes  strongly  granulated,  and  all  the  coloring  matter  seems  to 
be  concentrated  in  it,  the  surrounding  cell-substance  and  outline  of  the 
cell  becoming  almost  invisible;  after  a  time  the  cells  lose  their  color  alto- 
gether. The  cells  in  the  figure  (Fig.  71)  represent  the  successive  stages  of 
the  change.  A  similar  loss  of  color  occurs  in  the  red  cells  of  human  blood, 
which,  however,  from  the  absence  of  nuclei,  seem  to  disappear  entirely. 

Alkalies  cause  the  red  blood-cells  to  swell  and  finally  disappear. 

Chloroform  added  to  the  red  blood-cells  of  the  frog  causes  them  to 
part  with  their  haemoglobin;  the  stroma  of  the  cells  becomes  gradually 
broken  up.  A  similar  effect  is  produced  on  the  human  red  blood-cell. 

Tannin. — When  a  2  per  cent,  solution  of  tannic  acid  is  applied  to 
frog's  blood  it  causes  the  appearance  of  a  sharply-defined  little  knob,  pro- 
jecting from  the  free  surface:  the  coloring  matter- becomes  at  the  same 
time  concentrated  in  the  nucleus,  which  grows  more  distinct  (Fig.  72). 


78  HAND-BOOK    OF    PHYSIOLOGY. 

A  somewhat  similar  effect  is  produced  on  the  human  red  blood -cell. 
(Koberts.)  Magenta,  when  applied  to  the  red  blood-cells  of  the  [frog, 
produces  a  similar  little  knob  or  knobs,  at  the  same  time  staining  the 
nucleus  and  causing  the  discharge  of  the  haemoglobin.  (Roberts.)  The 
first  effect  of  the  magenta  is  to  cause  the  discharge  of  the  haemoglobin,, 
then  the  nucleus  becomes  suddenly  stained,  and  lastly  a  finely  granular 
matter  issues  through  the  wall  of  the  corpuscle,  becoming  stained  by  the 
magenta,  and  a  macula  is  formed  at  the  point  of  escape.  A  similar 
macula  is  produced  in  the  human  red  blood-cell. 

Boracic  acid. — A  2  per  cent,  solution  applied  to  nucleated  red  blood- 
cells  (frog)  will  cause  the  concentration  of  all  the  coloring  matter  in  the 
nucleus;  the  colored  body  thus  formed  gradually  quits  its  central  position, 
and  comes  to  be  partly,  sometimes  entirely,  protruded  from  the  surface 
of  the  now  colorless  cell  (Fig.  73).  The  result  of  this  experiment  led 
Briicke  to  distinguish  the  colored  contents  of  the  cell  (zooid)  from  its 
colorless  stroma  (oacoid).  When  applied  to  the  non-nucleated  mammalian 
corpuscle  its  effect  merely  resembles  that  of  other  dilute  acids. 

Gases — Carbonic  acid. — If  the  red  blood-cells  of  a  frog  be  first  exposed 


Vf* 

&  •» 


FIG.  73.  FIG.  74.  FIG.  75. 

to  the  action  of  water-vapor  (which  renders  their  outer  pellicle  more 
readily  permeable  to  gases),  and  then  acted  on  by  carbonic  acid,  the 
nuclei  immediately  become  clearly  defined  and  strongly  granulated;  when 
air  or  oxygen  is  admitted  the  original  appearance  is  at  once  restored. 
The  upper  and  lower  cell  in  Fig.  74  show  the  effect  of  carbonic  acid;  the 
middle  one  the  effect  of  the  re-admission  of  air.  These  effects  can  be 
reproduced  five  or  six  times  in  succession.  If,  however,  the  action  of  the 
carbonic  acid  be  much  prolonged,  the  granulation  of  the  nucleus  becomes 
permanent;  it  appears  to  depend  on  a  coagulation  of  the  paraglobulin. 
(Strieker.) 

Ammonia. — Its  effects  seem  to  vary  according  to  the  degree  of  con- 
centration. Sometimes  the  outline  of  the  corpuscles  becomes  distinctly 
crenated;  at  other  times  the  effect  resembles  that  of  boracic  acid,  while 
in  other  cases  the  edges  of  the  corpuscles  begin  to  break  up.  (Lankester.) 

Heat.—  The  effect  of  heat  up  to  120°— 140°  F.  (50°— 60°  C.)  is  to 
cause  the  formation  of  a  number  of  bud-like  processes  (Fig.  75). 

Electricity  causes  the  red  blood-corpuscles  to  become  crenated,  and 
at  length  mulberry-like.  Finally  they  recover  their  round  form  and 
become  quite  pale. 


THE    BLOOD. 


79 


The  general  conclusions  to  be  drawn  from  these  observations  have 
m  summed  up  as  follows  by  Prof.  Ray  Lankester: — 
"The  red  bipod-corpuscle  of  the  vertebrata  is  a  viscid,  and  at  the  same 
:ime  elastic  disc,  oval  or  round  in  outline,  its  surface  being  differentiated 
•mewhat  from  the  underlying  material,  and  forming  a  pellicle  or  mem- 
mine  of  great  tenuity,    not  distinguishable   with   the    highest  powers 
whilst  the  corpuscle  is  normal  and  living),  and  having  no  pronounced  inner 
limitation.     The  viscid  mass  consists  of  (or  rather  yields,  since  the  state 
>f  combination  of  the  components  is  not  known)  a  variety  of  albuminoid 
ind  other  bodies,  the  most  easily  separable  of  which  is  haemoglobin;  sec- 
mUy*  the  matter  which  segregates  to  form  Roberts'^  macula;  and  thirdly, 
residuary  stroma,  apparently  homogeneous  in  the  mammalia  (excepting 
far  as  the  outer  surface  or  pellicle  may  be  of  a  different  chemical 
lature),    but   containing   in  the   other  vertebrata    a  sharply   definable 
lucleus,  this  nucleus  being  already  differentiated,  but  not  sharply  deline- 
bed  during  life,  and  consisting  of,  or  separable  into,  at  least  two  com- 
ments, one  (paraglobulin)  precipitable  by  carbon  dioxide,  and  remov- 
ible  by  the  action  of  weak  ammonia;  the  other  pellucid,  and  not  gran- 
dated  by  acids." 

The  White  or  Colorless  Corpuscles. — In  human  olood  the  white 
>r    colorless    corpuscles    or    leucocytes  are   nearly   spherical   masses   of 
inular  protoplasm  without  cell  wall.     The  granular  appearance,  more 
larked  in  some  than  in  others  (vide  infra),  is  due  to  the  presence  of  par- 
:icles  probably  of  a  fatty  nature.     In  all  cases  one  or  more  nuclei  exist  in 
)h  corpuscle.     The  size  of  the  corpuscle  averages  ^--g-  of  an  inch  in 
liameter. 

In  health,  the  proportion  of  white  to  red  corpuscles,  which,  taking 
average,  is  about  1  to  500  or  600,  varies  considerably  even  in  the 
mrse  of  the  same  day.     The  variations  appear  to  depend  chiefly  on  the 
imouut  and  probably  also  on  the  kind  A  B 

)f  food  taken;  the  number  of  leuco- 
3ytes  being  very  considerably  increased 
iy  a  meal,  and  diminished  again  on 
sting.  Also  in  young  persons,  dur- 
ing pregnancy,  and  after  great  loss 
)f  blood,  there  is  a  larger  proportion 
)f  colorless  blood-corpuscles,  which 
probably  shows  that  they  are  more  rapidly  formed  under  these  circum- 
stances. In  old  age,  on  the  other  hand,  their  proportion  is  diminished. 

Varieties. — The  colorless  corpuscles  present  greater  diversities  of 
form  than  the  red  ones  do.  Two  chief  varieties  are  to  be  seen  in  human 
blood;  one  which  contains  a  considerable  number  of  granules,  and  the 
other  which  is  paler  and  less  granular.  In  size  the  variations  are  great, 
for  in  most  specimens  of  blood  it  is  possible  to  make  out,  in  addition  to 


FIG.  77.— A.  Three  colored  blood-corpuscles. 
B.  Three  colorless  blood-corpuscles  acted  on 
by  acetic  acid;  the  nuclei  are  very  clearly 
visible.  X  900. 


80  HAND-BOOK    OF    PHYSIOLOGY. 

the  full-sized  varieties,  a  number  of  smaller  corpuscles,  consisting  of  a 
large  spherical  nucleus  surrounded  by  a  variable  amount  of  more  or  less 
granular  protoplasm.  The  small  corpuscles  are,  in  all  probability,  the 
undeveloped  forms  of  the  others,  and  are  derived  from  the  cells  of  the 
lymph.  Besides  the  above-mentioned  varieties,  Schmidt  describes  another 
form  which  he  looks  upon  as  intermediate  between  the  colored  and  the 
colorless  forms,  viz.,  certain  corpuscles  which  contain  red  granules  of 
haemoglobin  in  their  protoplasm.  The  different  varieties  of  colorless  cor- 
puscles are  especially  well  seen  in  the  blood  of  frogs,  newts,  and  other 
cold-blooded  animals. 

Amoeboid  movement. — A  remarkable  property  of  the  colorless  cor- 
puscles consists  in  their  capability  of  spontaneously  changing  their  shape. 
This  was  first  demonstrated  by  Wharton  Jones  in  the  blood  of  the  skate. 
If  a  drop  of  blood  be  examined  with  a  high  power  of  the  microscope  on 
a  warm  stage,  or,  in  other  words,  under  conditions  by  which  loss  of  mois- 
ture is  prevented,  and  at  the  same  time  the  temperature  is  maintained  at 
about  that  of  the  blood  in  its  natural  state  within  the  walls  of  the  living 
vessels,  100°  F.  (37  "8°  C.),  the  colorless  corpuscles  will  be  observed  slowly 
altering  their  shapes,  and  sending  out  processes  at  various  parts  of  their 
circumference.  This  alteration  of  shape,  which  can  be  most  conveniently 


FIG.  78.— Human  colorless  blood-corpuscle,  showing  its  successive  changes  of  outline  within 
ten  minutes  when  kept  moist  on  a  warm  stage.    (Schofield.) 

studied  in  the  newt's  blood,  is  called  amoeboid,  inasmuch  as  it  strongly 
resembles  the  movement  of  the  lowly  organized  amccba.  The  processes 
which  are  sent  out  are  either  lengthened  or  withdrawn.  If  lengthened, 
the  protoplasm  of  the  whole  corpuscle  flows  as  it  were  into  its  process, 
and  the  corpuscle  changes  its  position;  if  withdrawn,  protrusion  of 
another  process  at  a  different  point  of  the  circumference  speedily  follows. 
The  change  of  position  of  the  corpuscle  can  also  take  place  by  a  flowing 
movement  of  the  whole  mass,  and  in  this  case  the  locomotion  is  compar- 
atively rapid.  The  activity  both  in  the  processes  of  change  of  shape  and 
also  of  change  in  position,  is  much  more  marked  in  some  corpuscles,  viz., 
in  the  granular  variety,  than  in  others.  Klein  states  that  in  the  newt's 
blood  the  changes  are  especially  likely  to  occur  in  a  variety  of  the  colorless 
corpuscle,  which  consists  of  masses  of  finely  granular  protoplasm  with 
jagged  outline,  containing  three  or  four  nuclei,  or  of  large  irregular 
masses  of  protoplasm  containing  from  five  to  twenty  nuclei.  Another 
phenomenon  may  be  observed  in  such  a  specimen  of  blood,  viz.,  the  divi- 
sion of  the  corpuscles,  which  occurs  in  the  following  way.  A  cleft  takes 
place  in  the  protoplasm  at  one  point,  which  becomes  deeper  and  deeper, 


THE    BLOOD.  81 

and  then  by  the  lengthening  out  and  attenuation  of  the  connection,  and 
finally  by  its  rupture,  two  corpuscles  result.  The  nuclei  have  previously 
undergone,  division.  The  cells  so  formed  are  said  to  be  remarkably  active 
in  their  movements.  Thus  we  see  that  the  rounded  form  which  the 
colorless  corpuscles  present  in  ordinary  microscopic  specimens  must  be 
looked  upon  as  the  shape  natural  to  a  dead  corpuscle  or  to  one  whose 
vitality  is  dormant  rather  than  as  the  shape  proper  to  one  living  and 
active. 

Action  of  re-agents  upon  the  colorless  corpuscles. — Feeding  the 
corpuscles. —  If  some  fine  pigment  granules,  e.g.,  powdered  vermilion, 
be  added  to  a  fluid  containing  colorless  blood-corpuscles,  on  a  glass  slide, 
these  will  be  observed,  under  the  microscope,  to  take  up  the  pigment.  In 
some  cases  colorless  corpuscles  have  been  seen  with  fragments  of  colored 
ones  thus  embedded  in  their  substance.  This  property  of  the  colorless 
corpuscles  is  especially  interesting  as  helping  still  further  to  connect  them 
with  the  lowest  forms  of  animal  life,  and  to  connect  both  with  the  organ- 
ized cells  of  which  the  higher  animals  are  composed. 

The  property  which  the  colorless  corpuscles  possess  of  passing  through 
the  walls  of  the  blood-vessels  will  be  described  later  on. 

Enumeration  of  the  Red  and  White  Corpuscles. — Several 
methods  are  employed  for  counting  the  blood-corpuscles,  most  of  them 
depending  upon  the  same  principle,  i.e.,  the  dilution  of  a  minute  volume 
of  blood  with  a  given  volume  of  a  colorless  solution  similar  in  specific 
gravity  to  blood  serum,  so  that  the  size  and  shape  of  the  corpuscles  is 
altered  as  little  as  possible.  A  minute  quantity  of  the  well-mixed  solu- 
tion is  then  taken,  examined  under  the  microscope,  either  in  a  flattened 
capillary  tube  (Malassez)  or  in  a  cell  (Hayem  &  Nachet,  Gowers)  of 
known  capacity,  and  the  number  of  corpuscles  in  a  measured  length  of 
the  tube,  or  in  a  given  area  of  the  cell  is  counted.  The  length  of  the 
tube  and  the  area  of  the  cell  are  ascertained  by  means  of  a  micrometer 
scale  in  the  microscope  ocular;  or  in  the  case  of  Gowers'  modification,  by 
the  division  of  the  cell  area  into  squares  of  known  size.  Having  ascer- 
tained the  number  of  corpuscles  in  the  diluted  blood,  it  is  easy  to  find 
out  the  number  in  a  given  volume  of  normal  blood.  Gowers'  modifica- 
tion of  Hayem  &  Cachet's  instrument,  called  by  him  "Hcvmacytometer," 
appears  to  be  the  most  convenient  form  of  instrument  for  counting  the 
corpuscles,  and  as  such  will  alone  be  described  (Fig.  79).  It  consists  of 
a  small  pipette  (A),  which,  when  filled  up  to  a  mark  on  its  stem,,,  holds 
995  cubic  millimetres.  It  is  furnished  with  an  india-rubber  tube  and 
glass  mouth-piece  to  facilitate  filling  and  emptying;  a  capillary  tube  (B) 
marked  to  hold  5  cubic  millimetres,  and  also  furnished  with  an  india- 
rubber  tube  and  mouthpiece;  a  small  glass  jar  (D)  in  which  the  dilution 
of  the  blood  is  performed;  a  glass  stirrer  (E)  for  mixing  the  blood 
thoroughly,  (F)  a  needle,  the  length  of  which  can  be  regulated  by  a, 
VOL.  I.— 6. 


82 


HAND-BOOK    OF    PHYSIOLOGY. 


.  screw;  a  brass  stage  plate  (c)  carrying  a  glass  slide,  on  which  is  a  cell 
•one-fifth  of  a  millimetre  deep,  and  the  bottom  of  which  is  divided  into 
one-tenth  millimetre  squares.  On  the  top  of  the  cell  rests  the  cover 
glass,  which  is  kept  in  its  place  by  the  pressure  of  two  springs  proceeding 
from  the  stage  plate.  A  standard  saline  solution  of  sodium  sulphate,  or 
similar  salt,  of  specific  gravity  1025,  is  made,  and  995  cubic  millimetres 
are  measured  by  means  of  the  pipette  into  the  glass  jar,  and  with  this  five 
cubic  millimetres  of  blood,  obtained  by  pricking  the  finger  with  a  needle, 
and  measured  in  the  capillary  pipette  (B),  are  thoroughly  mixed  by  the 


FIG.  79.— Haemacytometer. 


glass  stirring-rod.  A  drop  of  this  diluted  blood  is  then  placed  in  the  cell 
and  covered  with  a  cover-glass,  which  is  fixed  in  position  by  means  of  the 
two  lateral  springs.  The  preparation  is  then  examined  under  a  micro- 
scope with  a  power  of  about  400  diameters,  and  focussed  until  the  lines 
dividing  the  cell  into  squares  are  visible. 

After  a  short  delay,  the  red  corpuscles  which  have  sunk  to  the  bottom 
of  the  cell,  and  are  resting  on  the  squares,  are  counted  in  ten  squares, 
and  tlje  number  of  white  corpuscles  noted.  By  adding  together  the 
numbers  counted  in  ten  (one-tenth  millimetre)  squares  the  number  of 
corpuscles  in  one-cubic  millimetre  of  blood  is  obtained.  The  average 
number  of  corpuscles  per  each  cubic  millimetre  of  healthy  blood,  accord- 
ing to  Vierordt  and  Welcker,  is  5,000,000  in  adult  men,  and  rather  fewer 
in  women. 


THE    BLOOD. 


83 


Chemical  Composition  of  the  Blood  in  Bulk. — 
Water         ........ 

Solids- 
Corpuscles        ..... 

Proteids  ^of  serum) 

Fibrin  (of  clot)     .  ... 

Fatty  matters  (of  serum) 
Inorganic  salts  (of  serum) 
Gases,  kreatin,  urea  and  other  extractive  ) 
matter,  glucose  and  accidental  sub-  V 
stances ......) 


784 


130 
70 
2-2 
1-4 

G 


216 
1,000 


Chemical  Composition  of  the  Red  Corpuscles.— Analysis  of  a 

thousand  parts  of  moist  blood  corpuscles  shows  the  following  as  the 
result: — 


"Water 


.     688 
303.88 
8.12—312 


1,000 

Of  the  solids  the  most  important  is  Hcemoglobin,  the  substance  to 
•liich  the  blood  owes  its  color.  It  constitutes,  as  will  be  seen  from  the 
appended  Table,  more  than  90  per  cent,  of  the  organic  matter  of  the 
corpuscles.  Besides  haemoglobin  there  are  proteid :  and  fatty  matters,  the 
former  chiefly  consisting  of  globulins,  and  the  latter  of  cholesterin  and 
lecithin. 


In  1000  parts  organic  matter  are  found: — 

Haemoglobin 

Proteids  ..... 

Fats 


905-4 

86-7 

7-9 

1,000- 


Of  the  inorganic  salts  of  the  corpuscles,  with  the  iron  omitted — 

In  1000  parts  corpuscles  (Schmidt)  are  found  : — 

Potassium  Chloride    .        .  .  3-679 

Phosphate.        .  .  .     2-343 

sulphate         .  .  -132 

Sodium           ".......  .  "633 

Calcium          "  .  -094 

Magnesium     "  .  '060 

Soda .  .       -341 

7-282 


1  An  account  of  the  proteid  bodies,  etc.,  will  be  found  in  the  Appendix,  and  should 
"be  referred  to  for  explanation  of  the  terms  employed  in  the  text. 


84  HAND-BOOK    OF    PHYSIOLOGY. 

The  properties  of  hsemoglobin  will  be  considered  in  relation  to  the 
Gases  of  the  blood. 

Chemical  Composition  of  the  Colorless  Corpuscles. — In  conse- 
quence of  the  difficulty  of  obtaining  colorless  corpuscles  in  sufficient  num- 
ber to  make  an  analysis,  little  is  accurately  known  of  their  chemical  com- 
position; in  all  probability,  however,  the  stroma  of  the  corpuscles  is  made 
up  of  proteid  matter,  and  the  nucleus  of  nuclein,  a  nitrogenous  phos- 
phorus-containing body  akin  to  mucin,  capable  of  resisting  the  action  of 
the  gastric  juice.  The  proteid  matter  (globulin)  is  soluble  in  a  ten  per 
cent,  solution  of  sodium  chloride,  and  the  solution  is  precipitated  on  the 
addition  of  water,  by  heat  and  by  the  mineral  acids.  The  stroma  con- 
tains fatty  granules,  and  in  it  also  the  presence  of  glycogen  has  been 
demonstrated.  The  salts  of  the  corpuscles  are  chiefly  potassium,  and 
of  these  the  phosphate  is  in  greatest  amount. 

Chemical  Composition  of  the  Plasma  or  Liquor  Sanguinis.— 
The  liquid  part  of  the  blood,  the  plasma  or  liquor  sanguinis  in  which  the 
corpuscles  float,  may  be  obtained  in  the  ways  mentioned  under  the  head 
of  the  Coagulation  of  the  Blood.  In  it  are  the  fibrin  factors,  inasmuch 
as  when  exposed  to  the  ordinary  temperature  of  the  air  it  undergoes  coag- 
ulation and  splits  "up  into  fibrin  and  serum.  It  differs  from  the  serum 
in  containing  fibrinogen,  but  in  appearance  and  in  reaction  it  closely 
resembles  that  fluid;  its  alkalinity,  however,  is  less  than  that  of  the 
serum  obtained  from  it.  It  may  be  freed  from  white  corpuscles  by  filtra- 
tion at  a  temperature  below  41  °F.  (5°C.) 

Fibrin. — The  part  played  by  fibrin  in  the  formation  of  a  clot  has 
been  already  described  (p.  66),  and  it  is  only  necessary  to  consider  here 
its  general  properties.  It  is  a  stringy  elastic  substance  belonging  to  the 
proteid  class  of  bodies.  It  is  insoluble  in  water  and  in  weak  saline  solu- 
tions, it  swells  up  into  a  transparent  jelly  when  placed  in  dilute-hydro- 
chloric acid,  but  does  not  dissolve,  but  in  strong  acid  it  dissolves,  pro- 
ducing acid-albumin;1  it  is  also  soluble  on  boiling  in  strong  saline  solu- 
tions. Blood  contains  only  -2  per  cent,  of  fibrin.  It  can  be  converted 
by  the  gastric  or  pancreatic  juice  into  peptone.  It  possesses  the  power 
of  liberating  the  oxygen  from  solutions  of  hyclric  peroxide  HaOa.  This 
may  be  shown  by  dipping  a  few  shreds  of  fibrin  in  tincture  of  guaiacum 
and  then  immersing  them  in  a  solution  of  hyclric  peroxide.  The  fibrin 
becomes  of  a  bluish  color,  from  its  having  liberated  from  the  solution 
oxygen,  which  oxidizes  the  resin  of  guaiacum  contained  in  the  tincture 
and  thus  produces  the  coloration. 


1  The  use  of  the  two  words  albumen  and  albumin  may  need  explanation.  The 
former  is  the  generic,  word  which  may  include  several  albuminous  or  proteid  bodies, 
e.g.,  albumen  of  blood;  the  latter,  which  requires  to  be  qualified  by  another  word,  is 
the  specific  form,  and  is  applied  to  varieties,  e.g.,  egg-albumin,  serum-albumin. 


THE    BLOOD. 


85 


Salts  of  the  Plasma. — In  1000  parts  plasma  there  are: — 


Sodium  Chloride 

Soda      . 

Sodium  Phosphate 

Potassium  chloride  . 
"          sulphate  . 
Calcium   phosphate 
Magnesium  phosphate 


5-546 
1-532 
•271 
•359 
•281 
•298 
•218 

8.505 


Serum. — The  serum  is  the  liquid  part  of  the  blood  or  of  the  plasma 
remaining  after  the  separation  of  the  clot.  It  is  an  alkaline,  yellowish, 
transparent  fluid,  with  a  specific  gravity  of  from  1025  to  1032.  In  the 
usual  mode  of  coagulation,  part  of  the  serum  remains  in  the  clot,  and  the 
rest,  squeezed  from  the  clot  by  its  contraction,  lies  around  it.  Since  the 
contraction  of  the  clot  may  continue  for  thirty-six  or  more  hours,  the 
quantity  of  serum  in  the  blood  cannot  be  even  roughly  estimated  till  this 
period  has  elapsed.  There  is  nearly  as  much,  by  weight,  of  serum  as 
there  is  clot  in  coagulated  blood. 


Chemical  Composition  of  the  Serum. — 

Water 

Proteids: 

a.  Serum-albumin 

ft.  Paraglobulin          ...... 

Salts. 

Fats — including  fatty  acids,  cholesterin,  lecithin; 
and  some  soaps 

Grape  sugar  in  small  amount          ... 

Extractives — kreatin,  kreatinin,  urea,  etc. 

Yellow  pigment,  which  is  independent  of   haemo- 
globin        ........ 

Gases — small   amounts   of   oxygen,   nitrogen,   and 
carbonic  acid 


about    900 


80 


20 


1000 


Water. — The  water  of  the  serum  varies  in  amount  according  to  the 
amount  of  food,  drink,  and  exercise,  and  with  many  other  circumstances. 
Proteids. — a.  Serum-albumin  is  the  chief  proteid  found  in  serum. 

It  is  precipitated  on  heating  the  serum  to  140°  F.  (60°  C.),  and 
entirely  coagulates  at  (167°  F.  75°  C.),  and  also  by  the  addition  of  strong 
acids,  such  as  nitric  and  hydrochloric;  by  long  contact  with  alcohol  it  is 
precipitated.  It  is  not  precipitated  on  addition  of  ether,  and  so  differs 
from  the  other  native  albumin,  viz.,  ^(/-albumin.  When  dried  at  104°F. 
(40°  C.)  serum-albumin  is  a  brittle,  yellowish  substance,  soluble  in  water, 
possessing  a  Isevo-rotary  power  of  — 56°.  It  is  with  great  difficulty 


86  HAND-BOOK    OF    PHYSIOLOGY. 

freed  from  its  salts,  and  is  precipitated  by  solutions  Of  metallic  salts,  e.g. , 
of  mercuric  chloride,  copper  sulphate,  lead  acetate,  sodium  tungstate,  etc. 
If  dried  at  a  temperature  over  167°  F.  (75°  0.)  the  residue  is  insoluble 
in  water,  having  been  changed  into  coagulated  proteid. 

P.  Paraglobulin  can  be  obtained  as  a  white  precipitate  from  cold  serum 
by  adding  a  considerable  excess  of  water  and  passing  through  it  a  current 
of  carbonic  acid  gas  or  by  the  cautious  addition  of  dilute  acetic  acid.  It 
can  also  be  obtained  by  saturating  serum  with  crystallized  sulphate  mag- 
nesium or  chloride  sodium.  When  obtained  in  the  latter  way  precipita- 
tion seems  to  be  much  more  complete  than  by  means  of  the  former 
method.  Paraglobulin  belongs  to  the  class  of  proteids  called  globulins. 

The  proportion  of  serum-albumin  to  paraglobulin  in  human  blood 
serum  is  as  1'511  to  1. 

The  salts  of  sodium  predominate  in  serum  as  in  plasma,  and  of  these 
the  chloride  generally  forms  by  far  the  largest  proportion. 

Fats  are  present  partly  as  fatty  acids  and  partly  emulsified.  The 
fats  are  triolein,  tristearin,  and  tripalmitin.  The  amount  of  fatty  matter 
varies  according  to  the  time  after,  and  the  ingredients  of,  a  meal.  Of 
cliolesterin  and  lecithin  there  are  mere  traces. 

Grape  sugar  is  found  principally  in  the  blood  of  the  hepatic  vein,, 
about  one  part  in  a  thousand. 

The  extractives  vary  from  time  to  time;  sometimes  uric  and  hip- 
puric  acids  are  found  in  addition  to  urea,  kreatin  and  kreatinin.  Urea- 
exists  in  proportion  from  *02  to  *04  per  cent. 

The  yellow  pigment  of  the  serum  and  the  odorous  matter  which  gives 
the  blood  of  each  particular  animal  a  peculiar  smell,  have  not  yet  been 
properly  isolated. 

VARIATIONS  IN  HEALTHY  BLOOD  UNDER  DIFFERENT  CIRCUMSTANCES. 

The  conditions  which  appear  most  to  influence  the  composition  of  the 
blood  in  health  are  these:  Sex,  Pregnancy,  Age,  and  Temperament.  The 
composition  of  the  blood  is  also,  of  course,  much  influenced  by  diet. 

1.  Sex. — The  blood  of  men  differs  from  that  of  women,  chiefly  in  be- 
ing of  somewhat  higher  specific  gravity,  from  its  containing  a  relatively 
larger  quantity  of  red  corpuscles. 

2.  Pregnancy. — The   blood  of  pregnant  women  has  a  rather  lower 
specific  gravity  than  the  average,  from  deficiency  of  red  corpuscles.     The 
quantity  of  white  corpuscles,  on  the  other  hand,  and  of  fibrin,  is  in- 
creased. 

3.  Age. — It  appears  that  the  blood  of  the  foetus  is  very  rich  in  solid 
matter,  and  especially  in  red  corpuscles;  and  this  condition,  gradually 
diminishing,  continues  for  some  weeks  after  birth.     The  quantity  of  solid 
matter  then  falls  during  childhood  below  the  average,  again  rises  during 
adult  life,  and  in  old  age  falls  again. 


THE    BLOOD.  87 

4.  Temperament. — But  little  more  is  known  concerning  the  connection 
of  this  with  the  condition  of  the  blood,  than  that  there  appears  to  be  a 
relatively  larger  quantity  of  solid  matter,  and  particularly  of  red  corpuscles, 
in  those  of  a  plethoric  or  sanguineous  temperament. 

5.  Diet. — Such  differences  in  the  composition  of  the  blood  as  are  due  to 
the  temporary  presence  of  various  matters  absorbed  with  the  food  and 
drink,  as  well  as  the  more  lasting  changes  which  must  result  from  gener- 
ous or  poor  diet  respectively,  need  be  here  only  referred  to. 

Effects  of  Bleeding. — The  result  of  bleeding  is  to  diminish  the  specific 
gravity  of  the  blood;  and  so  quickly,  that  in  a  single  venesection,  the  portion 
of  blood  last  drawn  has  often  a  less  specific  gravity  than  that  of  the  blood 
that  flowed  first.  This  is,  of  course,  due  to  absorption  of  fluid  from  the 
tissues  of  the  body.  The  physiological  import  of  this  fact,  namely,  the 
instant  absorption  of  liquid  from  the  tissues,  is  the  same  as  that  of  the 
intense  thirst  wrhich  is  so  common  after  either  loss  of  blood,  or  the  ab- 
straction from  it  of  watery  fluid,  as  in  cholera,  diabetes,  and  the  like. 

For  some  little  time  after  bleeding,  the  want  of  red  corpuscles  is  well 
marked;  but  with  this  exception,  no  considerable  alteration  seems  to  be 
produce^  hi  the  composition  of  the  blood  for  more  than  a  very  short  time: 
the  loss  of  the  other  constituents,  including  the  pale  corpuscles,  being 
very  quickly  repaired. 


VARIATIONS  IN  THE  COMPOSITION  OF  THE  BLOOD,  IK  DIFFERENT  PAKTS 

OF  THE  BODY. 

The  composition  of  the  blood,  as  might  be  expected,  is  found  to  vary 
in  different  parts  of  the  body.  Thus  arterial  blood  differs  from  venous; 
and  although  its  composition  and  general  characters  are  uniform  through- 
out the  whole  course  of  the  systemic  arteries,  they  are  not  so  throughout 
the  venous  system, — the  blood  contained  in  some  veins  differing  remarka- 
bly from  that  in  others. 

Differences  between  Arterial  and  Venous  Blood. — The  differ- 
ences between  arterial  and  venous  blood  are  these: — 

(a.)  Arterial  blood  is  bright  red,  from  the  fact  that  almost  all  its 
haemoglobin  is  combined  with  oxygen  (Oxy haemoglobin,  or  scarlet  haemo- 
globin), while  the  purple  tint  of  venous  blood  is  due  to  the  deoxida- 
tion  of  a  certain  quantity  of  its  oxyhaemoglobin,  and  its  consequent  reduc- 
tion to  the  purple  variety  (Deoxidized,  or  purple  haemoglobin). 

(#.)  Arterial  blood  coagulates  somewhat  more  quickly. 

(c. }  Arterial  blood  contains  more  oxygen  than  venous,  and  less  carbonic 
acid. 

Some  of  the  veins  contain  blood  which  differs  from  the  ordinary  stand- 
ard considerably.  These  are  the  Portal,  the  Hepatic,  and  the  Splenic 
veins. 

Portal  vein. — The  blood  which  the  portal  vein  conveys  to  the  liver  is 
supplied  from  two  chief  sources;  namely,  that  in  the  gastric  and  mesen- 
teric  veins,  which  contains  the  soluble  elements  of  food  absorbed  from  the 


88  HAND-BOOK  OF  PHYSIOLOGY. 

stomach  and  intestines  during  digestion,  and  that  in  the  splenic  vein;  it 
must,  therefore,  combine  the  qualities  of  the  blood  from  each  of  these 
sources. 

The  blood  in  the  gastric  and  mesenteric  veins  will  vary  much  accord- 
ing to  the  stage  of  digestion  and  the  nature  of  the  food  taken,  and  can 
therefore  be  seldom  exactly  the  same.  Speaking  generally,  and  without 
considering  the  sugar,  dextrin,  and  other  soluble  matters  which  may  have 
been  absorbed  from  the  alimentary  canal,  this  blood  appears  to  be  defi- 
cient in  solid  matters,  especially  in  red  corpuscles,  owing  to  dilution  by  the 
quantity  of  water  absorbed,  to  contain  an  excess  of  albumin,  and  to  yield 
a  less  tenacious  kind  of  fibrin  than  that  of  blood  generally. 

The  blood  from  the  splenic  vein  is  generally  deficient  in  red  corpuscles, 
and  contains  an  unusually  large  proportion  of  proteids.  The  fibrin  ob- 
tainable from  the  blood  seems  to  vary  in  'relative  amount,  but  to  be  almost 
always  above  the  average.  The  proportion  of  colorless  corpuscles  is  also 
unusually  large.  The  whole  quantity  of  solid  matter  is  decreased,  the 
diminution  appearing  to  be  chiefly  in  the  proportion  of  red  corpuscles. 

The  blood  of  the  portal  vein,  combining  the  peculiarities  of  its  two 
factors,  the  splenic  and  mesenteric  venous  blood,  is  usually  of  lower 
specific  gravity  than  blood  generally,  is  more  watery,  contains  fewer  red 
corpuscles,  more  proteids,  and  yields  a  less  firm  clot  than  that  yielded  by 
other  blood,  owing  to  the  deficient  tenacity  of  its  fibrin. 

Guarding  (by  ligature  of  the  portal  vein)  against  the  possibility  of  an 
error  in  the  analysis  from  regurgitation  of  hepatic  blood  into  the  portal 
vein,  recent  observers  have  determined  that  hepatic  venous  blood  contains 
less  water,  albumen,  and  salts,  than  the  blood  of  the  portal  vein;  but  that 
it  yields  a  much  larger  amount  of  extractive  matter,  in  which  is  one  con- 
stant element,  namely,  grape-sugar,  which  is  found,  whether  saccharine 
or  farinaceous  matter  have  been  present  in  the  food  or  not. 


THE  GASES  OF  THE  BLOOD. 

The  gases  contained  in  the  blood  are  Carbonic  acid,  Oxygen,  and  Nitro- 
gen, 100  volumes  of  blood  containing  from  50  to  60  volumes  of  these  gases 
collectively. 

Arterial  blood  contains  relatively  more  oxygen  and  less  carbonic  acid 
than  venous.  But  the  absolute  quantity  of  carbonic  acid  is  in  both  kinds 
of  blood  greater  than  that  of  the  oxygen. 

Oxygen.                 Carbonic  Acid.  Nitrogen. 

Arterial  Blood      .     .     20  vol.  per  cent.  39  vol.  per  cent.  1  to  2  vols. 
Venous      " 

(from  muscles  at  rest)  8  to  12  "    "     "  46     "    "     "  1  to  2  vols. 

The  Extraction  of  the  Gases  from  the  Blood. — As  the  ordinary  air- 
pumps  are  not  sufficiently  powerful  for  the  purpose,  the  extraction  of  the 
gases  from  the  blood  is  accomplished  by  means  of  a  mercurial  air-pump, 
of  which  there  are  many  varieties,  those  of  Ludwig,  Alvergnidt,  Geissler, 
and  Sprengel  being  the  chief.  The  principle  of  action  in  all  is  much  the 


THE    BLOOD. 


89 


same.  Ludwig's  pump,  which  may  be  taken  as  a  type,  is  represented  in 
the  figure.  It  consists  of  two  fixed  globes,  C  and  F,  the  upper  one  com- 
municating by  means  of  the  stopcock  D,  and  a  stout  india-rubber  tube 
with  another  glass  globe,  L,  which  can  be  raised  or  lowered  by  means  of 
a  pulley;  it  also  communicates  by  means  of  a  stop-cock,  B,  and  a  bent 
glass  tube,  A,  with  a  gas  receiver  (not  represented  in  the  figure),  A  dip- 
ping into  a  bowl  of  mercury,  so  that  the  gas  may  be  received  over  mercury. 
The  lower  globe,  F,  communicates  with  C  by  means  of  the  stopcock,  E, 
with  /  in  which  the  blood  is  contained  by  the 
stopcock  G,  and  with  a  movable  glass  globe, 
M,  similar  to  Z,  by  means  of  the  stopcock,  H, 
and  the  stout  india-rubber  tube,  K. 

In  order  to  work  the  pump,  L  and  M  are 
filled  with  mercury,  the  blood  from  which  the 
gases  are  to  be  extracted  is  placed  in  the  bulb 
/,  the  stopcocks,  H,  E,  D,  and  B,  being  open, 
and  G  closed.  M  is  raised  by  means  of  the 
pulley  until  F  is  full  of  mercury,  and  the  air 
is  driven  out.  E  is  then  closed,  and  L  is  raised 
so  that  C  becomes  full  of  mercury,  and  the  air 
driven  off.  B  is  then  closed.  On  lowering  L 
the  mercury  runs  into  it  from  C,  and  a  vacuum 
is  established  in  0.  On  opening  E  and  lower- 
ing M,  a  vacuum  is  similarly  established  in  F; 
if  G  be  now  opened,  the  blood  in  /  will  enter 
into  ebullition,  and  the  gases  will  pass  off  into 
F  and  (7,  and  on  raising  M  and  then  L,  the 
stopcock  B  being  opened,  the  gas  is  driven 
through  A,  and  is  received  into  the  receiver 
over  mercury.  By  repeating  the  experiment 
several  times  the  whole  of  the  gases  of  the  speci- 
men of  blood  is  obtained,  and  may  be  estimated. 

The  Oxygen  of  the  Blood.— It  has  been 
found  that  a  very  small  proportion  of  the  oxygen 
which  can  be  obtained,  by  the  aid  of  the  mer- 
curial pump,  from  the  blood,  exists  in  a  state  of  simple  solution  in  the 
plasma.  If  the  gas  were  in  simple  solution,  the  amount  of  oxygen  in  any 
given  quantity  of  blood  exposed  to  any  given  atmosphere  ought  to  vary 
with  the  amount  of  oxygen  contained  in  the  atmosphere.  Since,  speak- 
ing generally,  the  amount  of  any  gas  absorbed  by  a  liquid  such  as  plasma 
would  depencl  upon  the  proportion  of  the  gas  in  the  atmosphere  to  which 
the  liquid  was  exposed  —  if  the  proportion  were  great,  the  absorption 
would  be  great;  if  small,  the  absorption  would  be  similarly  small.  The 
absorption  would  continue  until  the  proportion  of  the  gas  in  the  liquid 


FIG.  80.— Ludwig's  Mercurial 
Pump. 


90  HAND-BOOK    OF    PHYSIOLOGY, 

and  in  the  atmosphere  became  equal.  Other  things  would,  of  course,  in- 
fluence the  absorption,  such  as  the  kind  of  gas  employed,  nature  of  the 
liquid,  and  the  temperature  of  both,  but  cceteris  paribus,  the  amount  of 
a  gas  which  a  liquid  absorbs  depends  upon  the  proportion  of  the  gas — the 
so-called  partial  pressure — of  the  gas  in  the  atmosphere  to  which  the 
liquid  is  subjected.  And  conversely,  if  a  liquid  containing  a  gas  in  solu- 
tion be  exposed  to  an  atmosphere  containing  none  of  the  gas,  the  gas  will 
be  given  up  to  the  atmosphere  until  its  amount  in  the  liquid  and  in  the 
atmosphere  becomes  equal.  This  condition  is  called  a  condition  of  equal 
tensions.  The  condition  may  be  understood  by  a  simple  illustration.  A 
large  amount  of  carbonic  acid  gas  is  dissolved  in  a  bottle  of  water  by  ex- 
posing the  liquid  to  extreme  pressure  of  the  gas,  and  a  cork  is  placed  in 
the  bottle  and  wired  down.  The  gas  exists  in  the  water  in  a  condition  of 
extreme  tension,  and  therefore  there  is  a  tendency  of  the  gas  to  escape 
into  the  atmosphere,  in  order  that  the  tension  may  be  relieved;  this  causes 
the  violent  expulsion  of  the  cork  when  the  wire  is  removed,  and  if  the 
water  be  placed  in  a  glass  the  gas  will  continue  to  be  evolved  until  it  is 
almost  all  got  rid  of,  and  the  tension  of  the  gas  in  the  water  approximates 
to  that  of  the  atmosphere  in  which,  it  should  be  remembered,  the  carbon 
dioxide  is,  naturally,  in  very  small  amount,  viz.,  -04  per  cent.  Now  the 
oxygen  of  the  blood  does  not  obey  this  law  of  pressure.  For  if  blood 
which  contains  little  or  no  oxygen  be  exposed  to  a  succession  of  atmos- 
pheres containing  more  and  more  of  that  gas,  we  find  that  the  absorption 
is  at  first  very  great,  but  soon  becomes  relatively  very  small,  not  being 
therefore  regularly  in  proportion  to  the  increased  amount  (or  tension) 
of  the  oxygen  of  the  atmospheres,  and  that  conversely,  if  arterial  blood  be 
submitted  to  regularly  diminishing  pressures  of  oxygen,  at  first  very  little 
of  the  contained  oxygen  is  given  off  to  the  atmosphere,  then  suddenly 
the  gas  escapes  with  great  rapidity,  again  disobeying  the  law  of  pres- 
sures. 

Very  little  oxygen  can  be  obtained  from  serum  freed  from  blood  cor- 
puscles, even  by  the  strongest  mercurial  air-pump,  neither  can  serum  be 
made  to  absorb  a  large  quantity  of  that  gas;  but  the  small  quantity  which 
is  so  given  up  or  so  absorbed  follows  the  laws  of  absorption  according  to 
pressure.  .  , 

It  must  be,  therefore,  evident  that  the  chief  part  of  the  oxygen  is  con- 
tained in  the  corpuscles,  and  not  in  a  state  of  simple  solution.  The  chief 
solid  constituent  of  the  colored  corpuscles  is  haemoglobin,  which  consti- 
tutes more  than  90  per  cent,  of  their  bulk.  This  body  has  a  very  re- 
markable affinity  for  oxygen,  absorbing  it  to  a  very  definite  extent  under 
favorable  circumstances,  and  giving  it  up  when  subjected  to  the  action 
of  reducing  agents,  or  to  a  sufficiently  low  oxygen  pressure.  From  these 
facts  it  is  inferred  that  the  oxygen  of  the  blood  is  combined  with  haemo- 
globin, and  not  simply  dissolved;  but  inasmuch  as  it  is  comparatively  easy 


THE    BLOOD.  91 

to  cause  the  haemoglobin  to  give  up  its  oxygen,  it  is  believed  that  the 
oxygen  is  but  loosely  combined  with  the  substance. 

Haemoglobin.— Haemoglobin  is  a  crystallizable  body  which  constitutes 
by  fur  the  largest  portion  of  the  colored  corpuscles.  It  is  intimately  dis- 
tributed throughout  their  stroma,  and  must  be  dissolved  out  of  it  before 
it  will  undergo  crystallization.  Its  percentage  composition  is  C.  53*85; 
11.  7-32;  K".  16-17;  0.  21-84;  S.  -63;  Fe.  '42;  and  if  the  molecule  be  sup- 
posed to  contain  one  atom  of  iron  the  formula  would  be  C600,  H960,  N1M, 
Fe  Ss,  0179.  The  most  interesting  of  the  properties  of  haemoglobin  are  its 
powers  of  crystallizing  and  its  attraction  for  oxygen  and  other  gases. 

Crystals. — The  haemoglobin  of  the  blood  of  various  animals  possesses 
the  power  of  crystallizing  to  very  different  extents  (blood-crystals).  In  some 
animals  the  formation  of  crystals  is  almost  spontaneous,  whereas  in  others 
crystals  are  formed  either  with  great  difficulty  or  not  at  all.  Among  the 
animals  whose  blood  coloring-matter  crystallizes  most  readily  are  the 
guinea-pig,  rat,  squirrel,  and  dog;  and  in  these  cases  to  obtain  crystals  it 
is  generally  sufficient  to  dilute  a  drop  of  recently -drawn  blood  with  water 
and  expose  it  for  a  few  minutes  to  the  air.  Light  seems  to  favor  the  for- 
mation of  the  crystals.  In  many  instances  oth  ?r  means  must  be  adopted, 
e.f./.,  the  addition  of  alcohol,  ether,  or  chloroform,  rapid  freezing,  and 
then  thawing,  an  electric  current,  a  temperature  of  140°  F.  (60°  C.),  or 
the  addition  of  sodium  sulphate. 

Human  blood  crystallizes  with  difficulty,  as  does  also  that  of  the  ox, 
the  pig,  the  sheep,  and  the  rabbit. 


FIG.  81.— Crystals  of  oxy-hsemoglobin— prismatic  from  human  blood. 

The  forms  of  haemoglobin  crystals,  as  will  be  seen  from  the  appended 
figures,  differ  greatly. 

Haemogloblin  crystals  are  soluble  in  water.  Both  the  crystals  them- 
selves and  also  their  solutions  have  the  characteristic  color  of  arterial 
blood. 


yz  HAND-BOOK    OF    PHYSIOLOGY. 

A  dilute  solution  of  haemoglobin  gives  a  characteristic  appearance  with 
the  spectroscope.  Two  absorption  bands  are  seen  between  the  solar  lines 
D  and  E  (see  Plate),  one  toward  the  red,  with  its  middle  line  some  little 
way  to  the  blue  side  of  D,  is  very  intense,  but  narrower  than  the  other, 
which  lies  near  to  the  red  side  of  E.  Each  band  is  darkest  in  the  middle 
and  fades  away  at  the  sides.  As  the  strength  of  the  solution  increases  the 
bands  become  broader  and  deeper,  and  both  the  red  and  the  blue  ends  of 
the  spectrum  become  encroached  upon  until  the  bands  coalesce  to  form 
one  very  broad  band,  and  only  a  slight  amount  of  the  green  remains  un- 
absolved,  and  part  of  the  red,  and  on  further  increase  of  strength  the 
former  disappears. 

If  the  crystals  of  oxy-haemoglobin  be  subjected  to  a  mercurial  air-pump 
they  give  off  a  definite  amount  of  oxygen  (1  gramme  giving  off  1-59 


FIG.  82. 

FIG.  82. — Oxy-hsemoglobin  crystals — tetrahedral,  from  blood  of  the  guinea-pig. 
FIG.  83.— Hexagonal  oxy-heemoglobin  crystals,  from  blood  of  squirrel.    On  these  hexagonal 
plates,  prismatic  crystals,  grouped  in  a  stellate  manner,  not  unfrequently  occur  (after  Funke). 

c.cm.  of  oxygen),  and  they  become  of  a  purple  color;  and  a  solution  of  oxy- 
haemoglobin  may  be  made  to  give  up  oxygen  and  to  become  purple  in  a 
similar  manner. 

This  change  may  be  also  effected  by  passing  through  it  hydrogen  or 
nitrogen  gas,  or  by  the  action  of  reducing  agents,  of  which  Stokes's  fluid1 
is  the  most  convenient. 

With  the  spectroscope  a  solution  of  deoxidized  haemoglobin  is  found 
to  give  an  entirely  different  appearance  from  that  of  oxidized  haemoglo- 
bin. Instead  of  the  two  bands  at  D  and  E  we  find  a  single  broader  but 
fainter  band  occupying  a  position  midway  between  the  two,  and  at  the 


1  Stokes* 's  Fluid  consists  of  a  solution  of  ferrous  sulphate,  to  which  ammonia  has 
been  added  and  sufficient  tartaric  acid  to  prevent  precipitation.  Another  reducing 
agent  is  a  solution  of  stannous  chloride,  treated  in  a  way  similar  to  the  ferrous  sulphate, 
and  a  third  reagent  of  like  nature  is  an  aqueous  solution  of  ammonium  sulphide. 


THE    BLOOD.  93 

time  less  of  the  blue  end  of  the  spectrum  is  absorbed.  Even  in 
strong  solutions  this  latter  appearance  is  found,  thereby  differing  from 
the  strong  solution  of  oxidized  haemoglobin  which  lets  through  only  the 
red  and  orange  rays;  accordingly  to  the  naked  eye  the  one  (reduced 
haemoglobin  solution)  appears  purple,  the  other  (oxy-hsemoglobin  solu- 
tion) red.  The  deoxidized  crystals  or  their  solutions  quickly  absorb  oxy- 
gen on  exposure  to  the  air,  becoming  scarlet.  If  solutions  of  blood  be 
taken  instead  of  solutions  of  haemoglobin,  results  similar  to  the  whole  of 
the  foregoing  can  be  obtained. 

Venous  blood  never,  except  in  the  last  stages  of  asphyxia,  fails  to 
show  the  oxy-haemoglobin  bands,  inasmuch  as  the  greater  part  of  the 
haemoglobin  even  in  venous  blood  exists  in  the  more  highly  oxidized 
condition. 

Action  of  Gases  on  Haemoglobin. —  Carbonic  oxide,  passed  through 
a  solution  of  haemoglobin,  causes  it  to  assume  a  bluish  color,  and  the  spec- 
trum is  slightly  altered;  two  bands  are  still  visible,  but  are  somewhat 
nearer  the  blue  end  than  those  of  oxy-haemoglobin  (see  Plate).  The 
amount  of  carbonic  oxide  is  equal  to  the  amount  of  the  oxygen  displaced. 
Although  the  carbonic  oxide  gas  readily  displaces  oxygen,  the  reverse  is 
not  the  case,  and  upon  this  property  depends  the  dangerous  effect  of  coal 
gas  poisoning.  Coal  gas  contains  much  carbonic  oxide,  and  this  at  once, 
when  breathed,  combines  with  the  haemoglobin  of  the  blood,  producing 
a  compound  which  cannot  easily  be  reduced,  and  since  it  is  by  no  means 
an  oxygen  carrier,  death  may  result  from  suffocation  from  want  of  oxygen 
notwithstanding  the  free  entry  into  the  lungs  of  pure  air.  Crystals  of 
carbonic-oxide  haemoglobin  closely  resemble  those  of  oxyhaemoglobin. 

Nitric  oxide  produces  a  similar  compound  to  the  carbonic-oxide  haemo- 
globin, which  is  even  less  easily  reduced. 

Nitrous  oxide  reduces  oxyhaemoglobin,  and  therefore  leaves  the  reduced 
haemoglobin  in  a  condition  to  actively  take  up  oxygen. 

Sulphuretted  Hydrogen. — If  this  gas  be  passed  through  a  solution  of 
oxyhaemoglobin,  the  haemoglobin  is  reduced  and  an  additional  band 
appears  in  the  red.  If  the  solution  be  then  shaken  with  air,  the  two 
bands  of  oxyhaemoglobin  replace  that  of  reduced  haemoglobin,  but  the 
band  in  the  red  persists. 

PRODUCTS  OF  THE  DECOMPOSITION  OF  HAEMOGLOBIN. 

Methaemoglobin. — If  an  aqueous  solution  of  oxyhaemoglobin  be 
exposed  to  the  air  for  some  time,  its  spectrum  undergoes  a  change;  the 
two  D  and  E  bands  become  faint,  and  a  new  line  in  the  red  at  c  is  devel- 
oped. The  solution,  too,  has  become  brown  and  acid  in  reaction,  and  is 
precipitable  by  basic  lead  acetate.  This  change  is  due  to  the  decomposi- 
tion of  haemoglobin,  and  to  the  production  of  metlicernoglobin.  On  add- 


94  HAND-BOOK    OF    PHYSIOLOGY. 

ing  ammonium  sulphide,  reduced  haemoglobin  is  produced,  and  on  shaking 
this  up  with  air,  oxyhsemoglobin.  is  reproduced. 

Haematin. — By  the  action  of  heat,  or  of  acids  or  alkalies  in  the  pres- 
ence of  oxygen,  haemoglobin  can  be  split  up  into  a  substance  called 
H&matin,  which  contains  all  the  iron  of  the  haemoglobin  from  which  it 
was  derived,  and  a  proteid  residue.  Of  the  latter  it  is  impossible  to  say 
more  than  that  it  is  probably  made  up  of  one  or  more  bodies  of  the  globu- 
lin class.  If  there  be  no  oxygen  present,  instead  of  haematin  a  body  called 
hcemocliromogen  is  produced,  which,  however,  will  speedily  undergo  oxi- 
dation into  haematin. 

Haematin  is  a  dark  brownish  or  black  non-crystallizable  substance  of 
metallic  lustre.  Its  percentage  composition  is  C.  64-30;  H.  5 -50;  N.  9 -06; 
Fe,  8-82;  0.  12-32;  which  gives  the  formula  C68,  H70,  N8,  Fe2,  010  (Hoppe- 
Seyler).  It  is  insoluble  in  water,  alcohol,  and  ether;  soluble  in  the 
caustic  alkalies;  soluble  with  difficulty  in  hot  alcohol  to  which  is  added 
sulphuric  acid.  The  iron  may  be  removed  from  haematin  by  heating  it 
with  fuming  hydrochloric  acid  to  320°  F.  (160°  C.),  and  a  new  body, 
hcematoporpliyrin,  is  produced. 

In  acid  solution. — If  to  blood  an  excess  of  acetic  acid  be  added,  the 
color  alters  to  brown  from  decomposition  of  haemoglobin,  and' the  setting 
free  of  haematin;  by  shaking  this  solution  with  ether,  solution  of  the 
haematin  is  obtained.  The  spectrum  of  the  etherial  solution  shows  no 
less  than  four  absorption  bands,  viz.,  one  in  the  red  between  c  and  D,  one 
faint  and  narrow  close  to  D,  and  then  two  broader  bands,  one  between  D 
and  E,  and  another  nearly  midway  between  I  and  F.  The  first  band  is 
by  far  the  most  distinct,  and  the  acid  solution  of  haematin  without  ether 
shows  it  plainly. 

In  alkaline  solution. — The  absorption  band  is  still  in  the  red,  but 
nearer  to  D,  and  the  blue  end  of  the  spectrum  is  partially  absorbed  to  a 
considerable  extent.  If  a  reducing  agent  be  added,  two  bands  resembling 
those  of  oxyhaemoglobin,  but  nearer  to  the  blue,  appear;  this  is  the  spec- 
trum of  reduced  hcematin.  On  shaking  the  reduced  haematin  with  air  or 
oxygen  the  two  bands  are  replaced  by  the  single  band  of  alkaline 
haematin. 

Hsematoidin. — This  substance  is  found  in  the  form  of  yellowish 
crystals  in  old  blood  extravasations,  and  is  derived  from  the  haemoglobin. 
Their  crystalline  form  and  the  reaction  they  give  with  nitric  acid  seem  to 
show  them  to  be  identical  with  Bilirubin,  the  chief  coloring  matter  of 
the  Bile. 

Hsemin. — One  of  the  most  important  derivatives  of  nsematin  is 
Haemin.  It  is  usually  called  Hydrochlorate  of  Hcematin  (or  hydrochlo- 
ride),  but  its  exact  chemical  composition  is  uncertain.  Its  formula  is  C0fJ, 
H70,  N8,  Fe2,  010,  2  Hcl,  and  it  contains  5*18  per  cent,  of  chlorine,  but 
by  some  it  is  looked  upon  as  simply  crystallized  hamiatin.  Although 


THE    BLOOD.  95 

difficult  to  obtain  in  bulk,  a  specimen  may  be  easily  made  for  the  micro- 
scope in  the  following  way: — A  small  drop  of  dried  blood  is  finely  powdered 
with  a  few  crystals  of  common  salt  on  a  glass  slide,  and  spread  out;  a  cover 
<rlass  is  then  placed  upon  it,  and  glacial  acetic  acid  added  by  means  of  a 
capillary  pipette.  The  blood  at  once  turns  of  a  brownish  color.  The  slide 
is  then  heated,  and  the  acid  mixture  evaporated  to  dryness  at  a  high  tem- 
perature. The  excess  of  salt  is  washed  away  with  water  from  the  dried 
residue,  and  the  specimen  may  then  be  mounted.  A  large  number  of 
small,  dark,  reddish  black  crystals  of  a  rhombic  shape,  sometimes  ar- 
ranged in  bundles,  will  be  seen  if  the  slide  be  subjected  to  microscopic 
examination. 

The  formation  of  these  haemin  crystals  is  of  great  interest  and  impor- 
tance from  a  medico-legal  point  of  view,  as  it  constitutes  the  most  cer- 


FIG.  84.— Haematoidin  crystals.    (Frey.)  FIG.  85.— Hsemin  crystals.    (Frey.) 

tain  and  delicate  test  we  have  for  the  presence  of  blood  (not  of  necessity 
the  blood  of  man)  in  a  stain  on  clothes,  etc.  It  exceeds  in  delicacy  even 
the  spectroscopic  test. 

Estimation  of  Haemoglobin. — The  most  exact  method  is  by  the 
estimation  of  the  amount  of  iron  in  a  given  specimen  of  blood,  but  as  this 
is  a  somewhat  complicated  process,  a  method  has  been  proposed  which, 
though  not  so  exact,  has  the  advantage  of  simplicity.  This  consists  in 
comparing  the  color  of  a  given  small  amount  of  diluted  blood  with  gly- 
cerine jelly  tinted  with  carmine  and  .picrocarmine  to  represent  a  standard 
solution  of  blood  diluted  one  hundred  times.  The  amount  of  dilution 
which  the  given  blood  requires  will  thus  approximately  represent  the 
quantity  of  haemoglobin  it  contains.  (Gowers.) 

Distribution  of  Haemoglobin. — In  connection  with  the  ascertained 
function  of  haemoglobin  as  the  great  oxygen-carrier,  the  following  facts 
with  regard  to  its  distribution  are  of  importance. 

It  occurs  not  only  in  the  red  blood-cells  of  all  Vertebrata  (except  one 
fish  (leptocephalus)  whose  blood-cells  are  all  colorless),  but  also  in  similar 
cells  in  many  Worms:  moreover,  it  is  found  diffused  in  the  vascular  fluid 
of  some  other  worms  and  certain  Crustacea;  it  also  occurs  in  all  the  striated 
muscles  of  Mammals  and  Birds.  It  is  generally  absent  from  unstriated 


96  HAND-BOOK    OF    PHYSIOLOGY. 

muscle  except  that  of  the  rectum.  It  has  also  been  found  in  Mollusca  in 
certain  muscles  which  are  specially  active,  viz.,  those  which  work  the  rasp- 
like  tongue. 

In  the  muscles  of  Fish  it  has  hitherto  only  been  met  with  in  the  very 
active  muscle  which  moves  the  dorsal  fin  of  the  Hippocampus  (Ray  Lan- 
kester). 

The  Carbon  Dioxide  Gas  in  the  Blood.— Of  this  gas  in  the 
blood,  part  exists  in  a  state  of  simple  solution  in  the  serum,  and  the  rest 
in  a  state  of  weak  chemical  combination.  It  is  believed  that  the  latter 
is  combined  with  the  sodium  carbonate  in  a  condition  of  bicarbonate. 
Some  observers  consider  that  part  of  the  gas  is  associated  with  the  cor- 
puscles. 

The  Nitrogen  in  the  Blood. — It  is  believed  that  the  whole  of  the 
small  quantity  of  the  nitrogen  contained  in  the  blood  is  simply  dissolved 
in  the  fluid  plasma. 

DEVELOPMENT  OF  THE  BLOOD. 

The  first  formed  blood-corpuscles  of  the  human  embryo  differ  much 
in  their  general  characters  from  those  which  belong  to  the  later  periods 


Fift.  86. — Part  of  the  network  of  developing  blood-vessels  in  the  vascular  area  of  a  guinea-pig. 
U,  blood  corpuscles  becoming  free  in  an  enlarged  and  hollowed  out  part  of  the  network;  or,  process 
of  protoplasm.  (E.  A.  Schafer.) 

of  intra-uterine,  and  to  all  periods  of  extra-uterine  life.     Their  manner  of 
origin  is  at  first  very  simple. 

Surrounding  the  early  embryo  is  a  circular  area,  called  the  vascular 
area,  in  which  the  first  rudiments  of  the  blood-vessels  and  blood-corpuscles 
are  developed.  Here  the  nucleated  embryonal  cells  of  the  mesoblast,  from 
which  the  blood-vessels  and  corpuscles  are  to  be  formed,  send  out  processes 
in  various  directions,  and  these  joining  together,  form  an  irregular 
meshwork.  The  nuclei  increase  in  number,  and  collect  chiefly  in  the 
larger  masses  of  protoplasm,  but  partly  also  in  the  processes.  These 
nuclei  gather  around  them  a  certain  amount  of  the  protoplasm,  and  be- 


THE    BLOOD. 


97 


coming  colored,  form  the  red  blood  corpuscles.  The  protoplasm  of  the 
cells  and  their  branched  network  in  which  these  corpuscles  lie  then  be- 
comes hollowed  out  into  a  system  of  canals  enclosing  fluid,  in  which  the 
red  nucleated  corpuscles  float.  The  corpuscles  at  first  are  from  about 
•g-sW  ^0  TsW  °t  an  incn  i*1  diameter,  mostly  spherical,  and  with  granular 
contents,  and  a  well-marked  nucleus.  Their  nuclei,  which  are  about 
5^0-  of  an  inch  in  diameter,  are  central,  circular,  very  little  prominent 
on  the  surfaces  of  the  corpuscle,  and  apparently  slightly  granular  or  tu- 
berculated. 

The  corpuscles  then  strongly  resemble  the  colorless  corpuscles  of  the 
fully  developed  blood,  but  are  colored.  They  are  capable  of  amoeboid 
movement  and  multiply  by  division. 

When,  in  the  progress  of  embryonic  development,  the  liver  begins  to 
be  formed,  the  multiplication  of  blood-cells  in  the  whole  mass  of  blood 
ceases,  and  new  blood-cells  are  produced  by  this  organ,  and  also  by  the 
lymphatic  glands,  thymus  and  spleen.  These  are  at  first  colorless  and 
nucleated,  but  afterward  acquire  the  ordinary  blood- tinge,  and  resemble 
very  much  those  of  the  first  set.  They  also  multiply  by  division.  In 
whichever  way  produced,  however,  whether  from  the  original  formative 
cells  of  the  embryo,  or  by  the  liver  and  the  other  organs  mentioned 
above,  these  colored  nucleated  cells  begin  very  early  in  foetal  life  to  be 
mingled  with  colored  wcw-nucleated  corpuscles  resembling  those  of  the 
adult,  and  at  about  the  fourth  or  fifth  month  of  embryonic  existence  are 
completely  replaced  by  them. 

Origin  of  the  Mature  Red  Corpuscles. — The  non-nucleated  red 
corpuscles  may  possibly  be  derived  from  the  nucleated,  but  in  all  proba- 
bility are  an  entirely  new  formation,  and  the  methods  of  their  origin  are 


uniform  size;  /,  /',  developing  fat  cells.    (E.  A.  SchSfer.) 

the  following: — (1.)  During  foetal  life  and  possibly  in  some  animals,  e.g., 
the  rat,  which  are  born  in  an  immature  condition,  for  some  little  time  after 
birth,  the  blood  discs  arise  in  the  connective  tissue  cells  in  the  following 
way.  Small  globules,  of  varying  size,  of  coloring  matter  arise  in  the 
protoplasm  of  the  cells,  and  the  cells  themselves  become  branched,  their 
branches  joining  the  branches  of  similar  cells.  The  cells  next  become 
VOL.  I.— 7. 


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HAND-BOOK    OF    PHYSIOLOGY. 


vacuolated,  and  the  red  globules  are  free  in  a  cavity  filled  with  fluid  (Fig. 
88) ;  by  the  extension  of  the  cavity  of  the  cells  into  their  processes  anas- 
tomosing vessels  are  produced,  which  ultimately  join  with  the  previously 
existing  vessels,,  and  the  globules,  now  having  the  size  and  appearance  of 
the  ordinary  red  corpuscles,  are  passed  into  the  general  circulation.  This 
method  of  formation  is  called  intracellular  (Schafer). 


FIG.  88.— Further  development  of  blood-corpuscles  in  connective-tissue  cells  and  transformation 
of  the  latter  into  capillary  blood-vessels,  a,  an  elongated  cell  with  a  cavity  in  the  protoplasm  occu- 
pied by  fluid  and  by  blood-corpuscles  which  are  still  globular;  ft,  a  hollow  cell,  the  nucleus  of  which 
has  multiplied.  The  new  nuclei  are  arranged  around  the  wall  of  the  cavity,  the,  corpuscles  in  which 
have  now  become  discord;  c,  shows  the  mode  of  union  of  a  "hsemapoietic11  cell,  which,  in  this  in- 
stance, contains  only  one  corpuscle,  with  the  prolongation  ( bl )  of  a  previously  existing  vessel ;  a  and 
c,  from  the  new-born  rat;  6,  from  the  foetal  sheep.  (E.  A.  Schafer.) 

(2.)  From  the  white  corpuscles. — The  belief  that  the  red  corpuscles  are 
derived  from  the  white  is  still  very  general,  although  no  new  evidence 
has  been  recently  advanced  in  favor  of  this  view.  It  is,  however,  uncer- 
tain whether  the  nucleus  of  the  white  corpuscle  becomes  the  red  corpus- 
cle, or  whether  the  whole  white  corpuscle  is  bodily  converted  into  the  red 
by  the  gradual  clearing  up  of  its  contents  with  a  disappearance  of  the 
nucleus.  Probably  the  latter  view  is  the  correct  one. 


FIG.  89.—  Colored  nucleated  corpuscles,  from  the  red  marrow  of  the  guinea-pig.    (E.  A.  Schafer.) 


(3.)  From  the  medulla  of  bones.  —  Red  corpuscles  are  to  a  very  large 
extent  derived  during  adult  life  from  the  large  pale  cells  in  the  red  mar- 
row of  bones,  especially  of  the  ribs  (Figs.  44,  89).  These  cells  become 
colored  from  the  formation  of  haemoglobin  chiefly  in  one  part  of  their 
protoplasm.  This  colored  part  becomes  separated  from  the  rest  of  the 
cell  and  forms  a  red  corpuscle,  being  at  first  cup-shaped,  but  soon  taking  on 
the  normal  appearance  of  the  mature  corpuscle.  It  is  supposed  that  the 


THE    BLOOD.  99 

protoplasm  may  grow  up  again  and  form  a  number  of  red  corpuscles  in  a 
similar  way. 

(4.)  From  the  tissue  of  the  spleen. — It  is  probable  that  red  as  well  as 
white  corpuscles  may  be  produced  in  the  spleen. 

-(5.)  From  Microcytes. — Hayem  describes  the  small  particles  (micro- 
cytes),  previously  mentioned  as  contained  in  the  blood  (p.  75),  and  which 
he  calls  hsematoblasts,  as  the  precursors  of  the  red  corpuscles.  They  ac- 
quire color,  and  enlarge  to  the  normal  size  of  red  corpuscles. 

Without  doubt,  the  red  corpuscles  have,  like  all  other  parts  of  the 
organism,  a  tolerably  definite  term  of  existence,  and  in  a  like  manner  die 
and  waste  away  when  the  portion  of  work  allotted  to  them  has  been  per- 
formed. Neither  the  length  of  their  life,  however,  nor  the  fashion  of 
their  decay  has  been  yet  clearly  made  out.  It  is  generally  believed  that 
a  certain  number  of  the  red  corpuscles  undergo  disintegration  in  the 
spleen;  and  indeed  corpuscles  in  various  degrees  of  degeneration  have 
been  observed  in  this  organ. 

Origin  of  the  Colorless  Corpuscles.— The  colorless  corpuscles  of 
the  blood  are  derived  from  the  lymph  corpuscles,  being,  indeed,  indistin- 
guishable from  them;  and  these  come  chiefly  from  the  lymphatic  glands. 
Their  number  is  increased  by  division. 

Colorless  corpuscles  are  also  in  all  probability  derived  from  the  spleen 
and  thymus,  and  also  from  the  germinating  endothelium  of  serous  mem- 
branes, and  from  connective  tissue.  The  corpuscles  are  carried  into  the 
blood  either  with  the  lymph  and  chyle,  or  pass  directly  from  the  lymphatic 
tissue  in  which  they  have  been  formed  into  the  neighboring  blood-vessels. 

USES  OF  THE  BLOOD. 

1.  To  be  a  medium  for  the  reception  and  storing  of  matter  (ordinary 
food,  drink,  and  oxygen)  from  the  outer  world,  and  for  its  conveyance  to 
all  parts  of  the  body. 

2.  To  be  a  source  whence  the  various  tissues  of  the  body  may  take  the 
materials  necessary  for  their  nutrition  and   maintenance;    and  whence 
the  secreting  organs  may  take  the  constituents  of  their  various  secretions. 

3.  To  be  a  medium  for  the  absorption  of  refuse  matters  from  all  the 
tissues,  and  for  their  conveyance  to  those  organs  whose  function  it  is  to 
separate  them  and  cast  them  out  of  the  body. 

4.  To  warm  and  moisten  all  parts  of  the  body. 

USES  OF  THE  VARIOUS  CONSTITUENTS  OF  THE  BLOOD. 

Albumen. — Albumen,  which  exists  in  so  large  a  proportion  among  the 
.  chief  constituents  of  the  blood,  is  without  doubt  mainly  for  the  nourish- 
ment of  those  textures  which  contain  it  or  other  compounds  nearly  allied 
to  it. 


100  HAND-BOOK    OF    PHYSIOLOGY. 

Fibrin. — In  considering  the  functions  of  fibrin,  we  may  exclude  the 
notion  of  its  existence,  as  such,  in  the  blood  in  a  fluid  state,  and  of  its  use 
in  the  nutrition  of  certain  special  textures,  and  look  for  the  explanation 
of  its  functions  to  those  circumstances,  whether  of  health  or  disease, 
under  which  it  is  produced.  In  haemorrhage,  for  example,  the  formation 
of  fibrin  in  the  clotting  of  blood,  is  the  means  by  which,  at  least  for  a 
time,  the  bleeding  is  restrained  or  stopped;  and  the  material  or  blastema 
which  is  produced  for  the  permanent  healing  of  the  injured  part,  con- 
tains a  coagulable  material  identical,  or  very  nearly  so,  with  the  fibrin  of 
clotted  blood. 

Fatty  matters. — The  fatty  matters  of  the  blood  subserve  more  than 
one  purpose.  For  while  they  are  the  means,  in  part,  by  which  the  fat  of 
the  body,  so  widely  distributed  in  the  proper  adipose  and  other  textures, 
is  replenished,  they  also,  by  their  union  with  oxygen,  assist  in  maintain- 
ing the  temperature  of  the  body.  To  certain  secretions  also,  notably  the 
milk  and  bile,  fat  is  contributed. 

Saline  Matter. — The  uses  of  the  saline  constituents  of  the  blood  are, 
first,  to  enter  into  the  composition  of  such  textures  and  secretions  as  natu- 
rally contain  them,  and,  secondly,  to  assist  in  preserving  the  due  specific 
gravity  and  alkalinity  of  the  blood,  and  in  preventing  its  decomposition. 
The  phosphate  and  carbonate  of  sodium,  to  which  the  blood  owes  its 
alkaline  reaction,  increase  the  absorptive  power  of  the  serum  for  gases. 

Corpuscles. — The  important  use  of  the  red  corpuscles  is  in  relation  to- 
the  absorption  of  oxygen  in  the  lungs,  and  its  conveyance  to  the  tissues. 
How  far  the  red  corpuscles  are  actually  concerned  in  the  nutrition  of  the 
tissues  is  quite  unknown. 

The  relation  of  the  colorless  corpuscles  to  the  coagulation  of  the  blood 
has  been  already  considered;  of  their  functions,  other  than  are  concerned 
in  this  phenomenon,  and  in  the  regeneration  of  the  red  corpuscles, 
nothing  is  positively  known. 


CHAPTER  V. 

THE  CIRCULATION  OF  THE  BLOOD. 

THE  Heart  is  a  hollow  muscular  organ  containing  four  chambers,  two 
auricles  and  two  ventricles,  arranged  in  pairs.  On  each  side  (right  and 
left)  of  the  heart  is  an  auricle  joined  to  and  communicating  with  a  ven- 
tricle, but  the  chambers  on  the  right  side  do  not  directly  communicate 
with  those  on  the  left  side.  The  circulation  of  the  blood  is  chiefly 


FIG.  90.— Diagram  of  the  Circulation. 

carried  on  by  the  contraction  of  the  muscular  walls  of  these  chambers  of 
the  heart,  the  auricles  contracting  simultaneously,  and  their  contraction 
being  followed  by  the  simultaneous  contraction  of  the  ventricles.  The 
blood  is  conveyed  away  from  the  left  side  of  the  heart  by  the  arteries, 
and  returned  to  the  right  side  of  the  heart  by  the  veins,  the  arteries  and 
veins  being  continuous  with  each  other  at  one  end  by  means  of  the  heart, 
and  at  the  other  by  a  fine  network  of  vessels  called  the  capillaries.  The 


102 


HAND-BOOK    OF    PHYSIOLOGY. 


blood,  therefore,  in  its  passage  from  the  heart  passes  first  into  the  arteries, 
then  into  the  capillaries,  and  lastly  into  the  veins,  by  which  it  is  con- 
veyed back  again  to  the  heart,  thus  completing  a  revolution  or  circulation. 
The  right  side  of  the  heart  does  not  directly  communicate  with  the 
left  to  complete  the  entire  circulation,  but  the  blood  has  to  pass  from  the 
right  side  to  the  lungs,  through  the  pulmonary  artery,  then  through  the 
pulmonary  capillary-vessels  and  through  the  pulmonary  veins  to  the  left 
side  of  the  heart.  Thus  there  are  two  circulations  by  which  the  blood 
must  pass;  the  one,  a  shorter  circuit  from  the  right  side  of  the  heart  to 
the  lungs  and  back  again  to  the  left  side  of  the  heart;  the  other  and 
larger  circuit,  from  the  left  side  of  the  heart  to  all  parts  of  the  body  and 
back  again  to  the  right  side;  but  more  strictly  speaking,  there  is  only  one 
complete  circulation,  which  may  be  diagrammatically  represented  by  a 
double  loop,  as  in  the  accompanying  figure  (Fig.  90). 


R;ght  Lung. 


Pulmonary 
Artery. 


Left  Lung. 


Diaphragm. 

FIG.  91.— View  of  heart  and  lungs  in  situ.  The  front  portion  of  the  chest- wall,  and  the  outer  or 
parietal  layers  of  the  pleurae  and  pericardium  have  been  removed.  The  lungs  are  partly  collapsed. 

On  reference  to  this  figure,  and  noticing  the  direction  of  the  arrows, 
which  represent  the  course  of  the  stream  of  blood,  it  will  be  observed 
that  while  there  is  a  smaller  and  a  larger  circle,  both  of  which  pass 
through  the  heart,  yet  that  these  are  not  distinct,  one  from  the  other,  but 
are  formed  really  by  one  continuous  stream,  the  whole  of  which  must,  at 
one  part  of  its  course,  pass  through  the  lungs.  Subordinate  to  the  two 
principal  circulations,  the  Pulmonary  and  Systemic,  as  they  are  named, 
it  will  be  noticed  also  in  the  same  figure  that  there  is  another,  by  which 
a  portion  of  the  stream  of  blood  having  been  diverted  once  into  the  cap- 
illaries of  the  intestinal  canal,  and  some  other  organs,  and  gathered  up 
again  into  a  single  stream,  is  a  second  time  divided  in  its  passage  through 


CIRCULATION    OF    THE    BLOOD.  103 

the  liver,  before  it  finally  reaches  the  heart  and  completes  a  revolution. 
This  subordinate  stream  through  the  liver  is  called  the  Portal  circulation. 
The  Forces  concerned  in  the  Circulation  of  the  Blood. — (1) 
The  principal  force  provided  for  constantly  moving  the  blood  through 
the  course  of  the  circulation  is  that  of  the  muscular  substance  of  the 
heart;  other  assistant  forces  are  (2)  those  of  the  elastic  walls  of  the  arte- 
ries, (3)  the  pressure  of  the  muscles  among  which  some  of  the  veins  run, 
(4)  the  movements  of  the  walls  of  the  chest  in  respiration,  and  probably, 
to  some  extent,  (5)  the  interchange  of  relations  between  the  blood  and 
the  tissues  which  occurs  in  the  capillary  system  during  the  nutritive 
processes. 

THE  HEART. 

The  Pericardium. — The  heart  is  invested  by  a  membranous  sac — 
the  pericardium,  which  is  made  up  of  two  distinct  parts,  an  external 
fibrous  membrane,  composed  of  closely  interlacing  fibres,  which  has  its 
base  attached  to  the  diaphragm — both  to  the  central  tendon  and  to  the 
adjoining  muscular  fibres,  while  the  smaller  and  upper  end  is  lost  on  the 
large  blood-vessels  by  mingling  its  fibres  with  that  of  their  external  coats; 
and  an  internal  serous  layer,  which  not  only  lines  the  fibrous  sac,  but  also 
is  reflected  on  to  the  heart,  which  it  completely  invests.  The  part  which 
lines  the  fibrous  membrane  is  called  the  parietal  layer,  and  that  enclosing 
the  heart,  the  visceral  layer,  and  these  being  continuous  for  a  short  distance 
along  the  great  vessels  of  the  base  of  the  heart,  form  a  closed  sac,  the 
cavity  of  which  in  health  contains  just  enough  fluid  to  lubricate  the  two 
surfaces,  and  thus  enable  them  to  glide  smoothly  over  each  other  during 
the  movements  of  the  heart.  Most  of  the  vessels  passing  in  and  out  of 
the  heart  receive  more  or  less  investment  from  this  sac. 

The  heart  is  situated  in  the  chest  behind  the  sternum  and  costal  car- 
tilag3s,  being  placed  obliquely  from  right  to  left,  quite  two-thirds  to  the 
left  of  the  mid-sternal  line.  It  is  of  pyramidal  shape,  with  the  apex 
pointing  downward,  outward,  and  toward  the  left,  and  the  base  backward, 
inward,  and  toward  the  right.  It  rests  upon  the  diaphragm,  and  its 
pointed  apex,  formed  exclusively  of  the  left  side  of  the  heart,  is  in  con- 
tact with  the  chest  wall,  and  during  life  beats  against  it  at  a  point  called 
the  apex  beat,  situated  in  the  fifth  intercostal  space,  about  two  inches 
below  the  left  nipple,  and  an  inch  and  a  half  to  the  sternal  side.  The 
heart  is  suspended  in  the  chest  by  the  large  vessels  which  proceed  from 
its  base,  but,  excepting  the  base,  the  organ  itself  lies  free  in  the  sac  of 
the  pericardium.  The  part  which  rests  upon  the  diaphragm  is  flattened, 
and  is  known  as  the  posterior  surface,  whilst  the  free  upper  part  is  called 
the  anterior  surface.  The  margin  toward  the  left  is  thick  and  obtuse, 
whilst  the  lower  margin  toward  the  right  is  thin  and  acute. 


104 


HAISTD-BOOK    OF    PHYSIOLOGY. 


On  examination  of  the  external  surface  the  division  of  the  heart  into 
parts  which  correspond  to  the  chambers  inside  of  it  may  be  traced,  for  a 
deep  transverse  groove  called  the  auriculo-ventricular  groove  divides  the 
auricles  which  form  the  base  of  the  heart  from  the  ventricles  which  form 
the  remainder,  including  the  apex,  the  ventricular  portion  being  by  far 
the  greater;  and,  again,  the  inter-ventricular  groove  runs  between  the 


FIG.  92.— The  right  auricle  and  ventricle  opened,  and  a  part  of  their  right  and  anterior  walls  re- 
moved, so  as  to  show  their  interior.  %. — 1,  superior  vena  cava;  2,  inferior  vena  cava;  2',  hepatic 
veins  cut  short;  3,  right  auricle;  3',  placed  in  the  fossa  ovalis,  below  which  is  the  Eustachian  valve: 
3",  is  placed  close  to  the  aperture  of  the  coronary  vein;  +,  +,  placed  in  the  auriculo-ventricular 
groove,  where  a  narrow  portion  of  the  adjacent  walls  of  the  auricle  and  ventricle  has  been  preserved; 
4,  4,  cavity  of  the  right  ventricle,  the  upper  figure  is  immediately  below  the  semilunar  valves;  4', 
large  columna  carnea  or  musculus  papillaris;  5.  5',  5',  tricuspid  valve;  6,  placed  in  the  interior  of  the 
pulmonary  artery,  a  part  of  the  anterior  wall  of  that  vessel  having  been  removed,  and  a  narrow  por- 
tion of  it  preserved  at  its  commencement,  where  the  semilunar  valves  are  attached;  7,  concavity  of 
the  aortic  arch  close  to  the  cord  of  the  ductus  arteriosus ;  8,  ascending  part  or  sinus  of  the  arch  cov- 
ered at  its  commencement  by  the  auricular  appendix  and  pulmonary  artery;  9,  placed  between  the 
innominate  and  left  carotid  arteries;  10,  appendix  of  the  left  auricle;  11,  11,  the  outside  of  the  left 
ventricle,  the  lower  figure  near  the  apex.  (Allen  Thomson.) 

ventricles  both  front  and  back,  and  separates  the  one  from  the  other. 
The  anterior  groove  is  nearer  the  left  margin  and  the  posterior  nearer  the 
right,  as  the  front  surface  of  the  heart  is  made  up  chiefly  of  the  right 
ventricle  and  the  posterior  surface  of  the  left  ventricle.  In  the  furrows 
run  the  coronary  vessels,  which  supply  the  tissue  of  the  heart  itself  with 
blood,  as  well  as  nerves  and  lymphatics  imbedded  in  more  or  less  fatty 
tissue. 


CIRCULATION    OF    THE    BLOOD.  105 

The  Chambers  of  the  Heart. — The  interior  of  the  heart  is  divided 
by  a  partition  in  such  a  manner  as  to  form  two  chief  chambers  or  cavities 
— right  and  left.  Each  of  these  chambers  is  again  subdivided  into  an 
upper  and  a  Idwer  portion,  called  respectively,  as  already  incidentally  men- 
tioned, auricle  and  ventricle,  which  freely  communicate  one  with  the 
other;  the  aperture  of  communication,  however,  being  guarded  by  valves, 
so  disposed  as  to  allow  blood  to  pass  freely  from  the  auricle  into  the  ven- 
tricle, but  not  in  the  opposife  direction.  There  are  thus  four  cavities 
altogether  in  the  heart — two  auricles  and  two  ventricles;  the  auricle  and 
ventricle  of  one  side  being  quite  separate  from  those  of  the  other 
(Fig.  90). 

Right  Auricle. — The  right  auricle  is  situated  at  the  right  part  of 
the  base  of  the  heart  as  viewed  from  the  front.  It  is  a  thin  walled  cavity 
of  more  or  less  quadrilateral  shape  prolonged  at  one  corner  into  a  tongue- 
shaped  portion,  the  right  auricular  appendix,  which  slightly  overlaps  the 
exit  of  the  great  artery,  the  aorta,  from  the  heart. 

The  interior  is  smooth,  being  lined  with  the  general  lining  of  the 
heart,  the  endocardium,  and  into  it  open  the  superior  and  inferior  venas 
cavaB,  or  great  veins,  which  convey  the  blood  from  all  parts  of  the  body 
to  the  heart.  The  former  is  directed  downward  and  forward,  the  latter 
upward  and  inward;  between  the  entrances  of  these  vessels  is  a  slight 
tubercle  called  tubercle  of  Lower.  The  opening  of  the  inferior  cava  is 
protected  and  partly  covered  by  a  membrane  called  the  EustacMan  valve. 
In  the  posterior  wall  of  the  auricle  is  a  slight  depression  called  the 
fossa  ovalis,  which  corresponds  to  an  opening  between  the  right  and  left 
auricles  which  exists  in  foetal  life.  The  right  auricular  appendix  is  of 
oval  form,  and  admits  three  fingers.  Various  veins,  including  the  cor- 
onary sinus,  or  the  dilated  portion  of  the  right  coronary  vein,  open  into 
this  chamber.  In  the  appendix  are  closely  set  elevations  of  the  muscular 
tissue  covered  with  endocardium,  and  on  the  anterior  wall  of  the  auricle 
are  similar  elevations  arranged  parallel  to  one  another,  called  musculi 
pectin  ali. 

Right  Ventricle. — The  right  ventricle  occupies  the  chief  part  of  the 
anterior  surface  of  the  heart,  as  well  as  a  small  part  of  the  posterior  sur- 
face: it  forms  the  right  margin  of  the  heart.  It  takes  no  part  in  the 
formation  of  the  apex.  On  section  its  cavity,  in  consequence  of  the 
encroachment  upon  it  of  the  septum  ventriculorum,  is  semilunar  or  cre- 
scentic  (Fig.  94);  into  it  are  two  openings,  the  auriculo-ventricular  at 
the  base,  and  the  opening  of  the  pulmonary  artery  also  at  the  base,  but 
more  to  the  left;  the  part  of  the  ventricle  leading  to  it  is  called  the  conus 
arteriosus  or  infundibulum;  both  orifices  are  guarded  by  valves,  the 
former  called  tricuspid  and  the  latter  semilunar  or  sigmoid.  In  this 
ventricle  are  also  the  projections  of  the  muscular  tissue  called  columnce 
carnece  (described  at  length  p.  110). 


106 


HAND-BOOK    OF    PHYSIOLOGY. 


Left  Auricle. — The  left  auricle  is  situated  at  the  left  and  posterior 
part  of  the  base  of  the  heart,  and  is  best  seen  from  behind.  It  is  quadri- 
lateral, and  receives  on  either  side  two  pulmonary  veins.  The  auricular 
appendix  is  the  only  part  of  the  auricle  seen  from  the  front,  and  corre- 


FIG.  93. — The  left  auricle  and  ventricle  opened,  and  a  part  of  their  anterior  and  left  walls  re- 
moved. H-— The  pulmonary  artery  has  been  divided  at  its  commencement;  the  opening  into  the  left 
ventricle  carried  a  short  distance  into  the  aorta  between  two  of  the  segments  of  the  sernilunar  valves, 
and  the  left  part  of  the  auricle  with  its  appendix  has  been  removed.  The  right  auricle  is  out  of  view. 
1,  the  two  right  pulmonary  veins  cut  short;  their  openings  are  seen  within  the  auricle;  1',  placed 
within  the  cavity  of  the  auricle  on  the  left  side  of  the  septum  and  on  the  part  which  forms  the  re- 
mains of  the  valve  of  the  foramen  ovale,  of  which  the  crescentic  fold  is  seen  toward  the  left  hand  of 
1' ;  2,  a  narrow  portion  of  the  wall  of  the  auricle  and  ventricle  preserved  round  the  auriculo- ven- 
tricular orifice;  3,  3',  the  cut  surface  of  the  walls  of  the  ventricle,  seen  to  become  very  much  thinner 
toward  3",  at  the  apex;  4,  a  small  part  of  the  anterior  wall  of  the  left  ventricle  which  has  been  pre- 
served with  the  principal  anterior  columna  carnea  or  musculus  papillaris  attached  to  it;  5, 5,  musculi 
papillares;  5',  the  left  side  of  the  septum,  between  the  two  ventricles,  within  the  cavity  of  the  left 
ventricle;  6,  6',  the  mitral  valve;  7,  placed  in  the  interior  of  the  aorta  near  its  commencement  and 
above  the  three  segments  of  its  semilunar  valve  which  are  hanging  loosely  together;  7',  the  exterior 
of  the  great  aortic  sinus ;  8,  the  root  of  the  pulmonary  artery  and  its  semilunar  valves ;  8'.  the  sepa- 
rated portion  of  the  pulmonary  artery  remaining  attached  to  the  aorta  by  9,the  cord  of  the  ductus 
arteriosus;  10,  the  arteries  rising  from  the  summit  of  the  aortic  arch.  (Allen  Thomson.) 


spends  with  that  on  the  right  side,  but  is  thicker,  and  the  interior  is  more 
smooth.  The  left  auricle  is  only  slightly  thicker  than  the  right,  the  dif- 
ference being  as  1 J  lines  to  1  line.  The  left  auriculo-ventricular  orifice 
is  oval,  and  a  little  smaller  than  that  on  the  right  side  of  the  heart. 


CIRCULATION    OF    THE    BLOOD. 


107 


Fro.  94. — Transverse  section  of  bullock's 
heart  in  a  state  of  cadaveric  rigidity,  a, 
cavity  of  left  ventricle.  6,  cavity  of  right- 
ventricle.  (Dalton.) 


There  is  a  slight  vestige  of  the  foramen  between  the  auricles,  which 
exists  in  fatal  life,  on  the  septum  between  them. 

Left  Ventricle. — Though  taking  part  to  a  comparatively  slight 
extent  in  the  anterior  surface,  the  left  ventricle  occupies  the  chief  part  of 
the  posterior  surface.  In  it  are  two  openings  very  close  together,  viz. 
the  auriculo-ventricular  and  the  aortic,  guarded  by  the  valves  corre- 
sponding to  those  of  the  right  side  of 
the  heart,  viz.  the  bicuspid  or  mitral 
and  the  semilunar  or  sigmoid.  The  first 
opening  is  at  the  left  and  back  part  of 
the  base  of  the  ventricle,  and  the  aortic 
in  front  and  toward  the  right.  In  this 
ventricle,  as  in  the  right,  are  the  co- 
lumnae  carneae,  which  are  smaller  but 
more  closely  reticulated.  They  are 
chiefly  found  near  the  apex  and  along 
the  posterior  Avail.  They  will  be  again 
referred  to  in  the  description  of  the  valves.  The  walls  of  the  left  ven- 
tricle, which  are  nearly  half  an  inch  in  thickness,  are,  with  the  exception 
of  the  apex,  twice  or  three  times  as  thick  as  those  of  the  right. 

Capacity  of  the  Chambers. — The  capacity  of  the  two  ventricles 
is  about  four  to  six  ounces  of  blood,  the  whole  of  which  is  impelled  into 
their  respective  arteries  at  each  contraction.  The  capacity  of  the  auricles 
is  rather  less  than  that  of  the  ventricles:  the  thickness  of  their  walls  is 
considerably  less.  The  latter  condition  is  adapted  to  the  small  amount 
of  force  which  the  auricles  require  in  order  to  empty  themselves  into  their 
adjoining  ventricles;  the  former  to  the  circumstance  of  the  ventricles 
being  partly  filled  with  blood  before  the  auricles  contract. 

Size  and  Weight  of  the  Heart. — The  heart  is  about  5  inches 
long,  3£  inches  greatest  width,  and  2|-  inches  in  its  extreme  thickness. 
The  average  weight  of  the  heart  in  the  adult  is  from  9  to  10  ounces;  its 
weight  gradually  increasing  throughout  life  till  middle  age;  it  diminishes 
in  old  age. 

Structure. — The  walls  of  the  heart  are  constructed  almost  entirely 
of  layers  of  muscular  fibres;  but  a  ring  of  connective  tissue,  to  which  some 
of  the  muscular  fibres  are  attached,  is  inserted  between  each  auricle  and 
ventricle,  and  forms  the  boundary  of  the  auriculo-ventricular  opening. 
Fibrous  tissue  also  exists  at  the  origins  of  the  pulmonary  artery  and  aorta. 

The  muscular  fibres  of  each  auricle  are  in  part  continuous  with  those 
of  the  other,  and  partly  separate;  and  the  same  remark  holds  true  for  the 
ventricles.  The  fibres  of  the  auricles  are,  however,  quite  separate  from 
those  of  the  ventricles,  the  bond  of  connection  between  them  being  only 
the  fibrous  tissue  of  the  auriculo-ventricular  openings. 

The  muscular  fibres  of  the  heart,  unlike  those  of  most  of  the  involun- 


108 


HAND-BOOK    OF    PHYSIOLOGY. 


tary  muscles,  are  striated;  but  although,  in  this  respect,  they  resemble 
the  skeletal  muscles,  they  have  distinguishing  characteristics  of  their  own. 
The  fibres  which  lie  side  by  side  are  united  at  frequent  intervals  by  short 
branches  (Fig.  95).  The  fibres  are  smaller  than  those  of  the  ordinary 
striated  muscles,  and  their  striation  is  less  marked.  No  sarcolemma  can 
be  discerned.  The  muscle-corpuscles  are  situate  in  the  middle  of  the 
substance  of  the  fibre;  and  in  correspondence  with  these  the  fibres  appeal- 
under  certain  conditions  subdivided  into  oblong  portions  or  "cells,"  the 
off-sets  from  which  are  the  means  by  which  the  fibres  anastomose  one 
with  another  (Fig.  96). 

Endocardium. — As  the  heart  is  clothed  on  the  outside  by  a  thin 
transparent  layer  of  pericardium,  so  its  cavities  are  lined  by  a  smooth  and 


FIG.  95. 


FIG. 


FIG.  95.— Network  of  muscular  fibres  (striated)  from  the  heart  of  a  pig.    The  nuclei  of  the  mus- 
cle-corpuscles are  well  shown.     X  450.    (Klein  and  Noble  Smith.) 
FIG.  96.— Muscular  fibre  cells  from  the  heart.    (E.  A.  Shafer.) 

shining  membrane,  or  endocardium,  which  is  directly  continuous  with  the 
internal  lining  of  the  arteries  and  veins.  The  endocardium  is  composed  of 
connective  tissue  with  a  large  admixture  of  elastic  fibres;  and  on  its  inner 
surface  is  laid  down  a  single  tessellated  layer  of  flattened  endothelial  cells. 
Here  and  there  unstriped  muscular  fibres  are  sometimes  found  in  the  tis- 
sue of  the  endocardium. 

Course  of  the  Blood  through  the  Heart. — The  arrangement  of 
the  heart's  valves  is  such  that  the  blood  can  pass  only  in  one  direction, 
and  this  is  as  follows  (Fig.  97): — From  the  right  auricle  the  blood  passes 
into  the  right  ventricle,  and  thence  into  the  pulmonary  artery,  by  which 
it  is  conveyed  to  the  capillaries  of  the  lungs.  From  the  lungs  the  blood, 
which  is  now  purified  and  altered  in  color,  is  gathered  by  the  pulmonary 


CIRCULATION    OF    THE    BLOOD.  109 

veins  and  taken  to  the  left  auricle.  From  the  left  auricle  it  passes  into 
the  left  ventricle,  and  thence  into  the  aorta,  by  which  it  is  distributed  to 
the  capillaries  of  every  portion  of  the  body.  The  branches  of  the  aorta, 
from  being  distributed  to  the  general  system,  are  called  systemic  arteries; 
and  from  these  the  blood  passes  into  the  systemic  capillaries,  where  it 
again  becomes  dark  and  impure,  and  thence  into  the  branches  of  the 
fii/xfanii'  veins,  which,  forming  by  their  union  two  large  trunks,  called 
the  superior  and  inferior  vena  cava,  discharge  their  contents  into  the  right 
auricle,  whence  we  supposed  the  blood  to  start. 

The  Valves  of  the  Heart. — The  valve  between  the  right  auricle 
and  ventricle  is  named  tricuspid  (5,  Fig.  99),  because  it  presents  three 
principal  cusps  or  subdivisions,  and  that  between  the  left  auricle  and  ven- 


FIG.  97.— Diagram  of  the  circulation  through  the  heart.    (Dalton.) 


tricle  bicuspid  (or  mitral),  because  it  has  two  such  portions  (6,  Fig.  93). 
But  in  both  valves  there  is  between  each  two  principal  portions  a  smaller 
one;  so  that  more  properly,  the  tricuspid  may  be  described  as  consisting 
of  six,  and  the  mitral  of  four,  portions.  Each  portion  is  of  triangular 
form,  its  apex  and  sides  lying  free  in  the  cavity  of  the  ventricle,  and  its 
base,  which  is  continuous  with  the  bases  of  the  neighboring  portions,  so 
as  to  form  an  annular  membrane  around  the  auriculo -ventricular  open- 
ing, being  fixed  to  a  tendinous  ring  which  encircles  the  orifice  between 
the  auricle  and  ventricle  and  receives  the  insertions  of  the  muscular  fibres 
of  both.  In  each  principal  cusp  may  be  distinguished  a  middle-piece, 
extending  from  its  base  to  its  apex,  and  including  about  half  its  width, 
which  is  thicker,  and  much  tougher  and  tighter  than  the  border-pieces 
or  edges. 

While  the  bases  of  the  several  portions  of  the  valves  are  fixed  to  the 


110  HAND-BOOK    OF    PHYSIOLOGY. 

tendinous  rings,  their  ventricular  surfaces  and  borders  are  fastened  by 
slender  tendinous  fibres,  the  cliordce  tendinece,  to  the  walls  of  the  ventri- 
cles, the  muscular  fibres  of  which  project  into  the  ventricular  cavity  in 
the  form  of  bundles  or  columns — the  columncs  carnece.  These  columns 
are  not  all  of  them  alike,  for  while  some  of  them  are  attached  along  their 
whole  length  on  one  side  and  by  their  extremities,  others  are  attached 
only  by  their  extremities;  and  a  third  set,  to  which  the  name  musculi 
papillares  has  been  given,  are  attached  to  the  wall  of  the  ventricle  by 
one  extremity  only,  the  other  projecting,  papilla-like,  into  the  cavity  of 
the  ventricle  (5,  Fig.  93),  and  having  attached  to  it  clwrdce  tendinew. 
Of  the  tendinous  cords,  besides  those  which  pass  from  the  walls  of  the 
ventricle  and  the  musculi  papillares  to  the  margins  of  the  valves,  there 
are  some  of  especial  strength,  which  pass  from  the  same  parts  to  the  edges 
of  the  middle  and  thicker  portions  of  the  cusps  before  referred  to.  The 
ends  of  these  cords  are  spread  out  in  the  substance  of  the  valve,  giving 
its  middle  piece  its  peculiar  strength  and  toughness;  and  from  the  sides 
numerous  other  more  slender  and  branching  cords  are  given  off,  which 
are  attached  all  over  the  ventricular  surface  of  the  adjacent  border-pieces 
of  the  principal  portions  of  the  valves,  as  well  as  to  those  smaller  portions 
which  have  been  mentioned  as  lying  between  each  two  principal  ones. 
Moreover,  the  musculi  papillares  are  so  placed  that,  from  the  summit  of 
each,  tendinous  cords  proceed  to  the  adjacent  halves  of  two  of  the  prin- 
cipal divisions,  and  to  one  intermediate  or  smaller  division,  of  the  valve. 

The  preceding  description  applies  equally  to  the  mitral  and  tricuspid 
valve;  but  it  should  be  added  that  the  mitral  is  considerably  thicker  and 
stronger  than  the  tricuspid,  in  accordance  with  the  greater  force  which 
it  is  called  upon  to  resist. 

It  has  been  already  said  that  while  the  ventricles  communicate,  on  the 
one  hand,  with  the  auricles,  they  communicate,  on  the  other,  with  the 
large  arteries  which  convey  the  blood  away  from  the  heart;  the  right  ven- 
tricle with  the  pulmonary  artery  (6,  Fig.  93),  which  conveys  blood  to  the 
lungs,  and  the  left  ventricle  with  the  aorta,  which  distributes  it  to  the 
general  system  (7,  Fig.  93).  And  as  the  auriculo-ventricular  orifice  is 
guarded  by  valves,  so  are  also  the  mouths  of  the  pulmonary  artery,  and 
aorta  (Figs.  93,  99). 

The  semilunar  valves,  three  in  number,  guard  the  orifice  of  each  of 
these  two  arteries.  They  are  nearly  alike  on  both  sides  of  the  heart;  but 
those  of  the  aorta  are  altogether  thicker  and  more  strongly  constructed 
than  those  of  the  pulmonary  artery,  in  accordance  with  the  greater  pres- 
sure which  they  have  to  withstand.  Each  valve  is  of  semilunar  shape,  its 
convex  margin  being  attached  to  a  fibrous  ring  at  the  place  of  junction 
of  the  artery  to  the  ventricle,  .and  the  concave  or  nearly  straight  border 
being  free,  so  that  each  valve  forms  a  little  pouch  like  a  watch-pocket 
(7,  Fig.  93).  In  the  centre  of  the  free  edge  of  the  valve,  which  contains 


CIRCULATION    OF    THE    BLOOD.  Ill 

a  fine  cord  of  fibrous  tissue,  is  a  small  fibrous  nodule,  the  corpus  Arantii, 
and  from  this  and  from  the  attached  border  fine  fibres  extend  into  every 
part  of  the  mid  substance  of  the  valve,  except  a  small  lunated  space  just 
within  the  free  edge,  on  each  side  of  the  corpus  Arantii.  Here  the  valve 
is  thinnest,  and  composed  of  little  more  than  the  endocardium.  Thus 
constructed  and  attached,  the  three  semilunar  valves  are  placed  side  by 
side  around  the  arterial  orifice  of  each  ventricle,  so  as  to  form  three  little 
pouches,  which  can  be  separated  by  the  blood  passing  out  of  the  ventricle, 
but  which  immediately  afterward  are  pressed  together  so  as  to  prevent 
any  return  (7,  Fig.  93,  and  7,  Fig.  99).  This  will  be  again  referred  to. 
Opposite  each  of  the  semilunar  cusps,  both  in  the  aorta  and  pulmonary 
artery,  there  is  a  bulging  outward  of  the  wall  of  the  vessel:  these  bulg- 
ings  are  called  the  sinuses  of  Valsalva. 

Structure  of  the  Valves. — The  valves  of  the  heart  are  formed  es- 
sentially of  thick  layers  of  closely  woven  connective  and  elastic  tissue,  over 
which,  on  every  part,  is  reflected  the  endocardium. 

THE  ACTION  OF  THE  HEART. 

The  heart's  action  in  propelling  the  blood  consists  in  the  successive 
alternate  contraction  (systole)  and  relaxation  (diastole)  of  the  muscular 
walls  of  its  two  auricles  and  two  ventricles. 

Action  of  the  Auricles. — The  description  of  the  action  of  the  heart 
may  best  be  commenced  at  that  period  in  each  action  which  immedi- 
ately precedes  the  beat  of  the  heart  against  the  side  of  the  chest.  For  at 
this  time  the  whole  heart  is  in  a  passive  state,  the  walls  of  both  auricles 
and  ventricles  are  relaxed,  and  their  cavities  are  being  dilated.  The  auri- 
cles are  gradually  filling  with  blood  flowing  into  them  from  the  veins;  and 
a  portion  of  this  blood  passes  at  once  through  them  into  the  ventricles, 
the  opening  between  the  cavity  of  each  auricle  and  that  of  its  correspond- 
ing ventricle  being,  during  all  the  pause,  free  and  patent.  The  auricles, 
however,  receiving  more  blood  than  at  once  passes  through  them  to  the 
ventricles,  become,  near  the  end  of  the  pause,  fully  distended;  and  at  the 
end  of  the  pause,  they  contract  and  expel  their  contents  into  the  ventricles. 

The  contraction  of  the  auricles  is  sudden  and  very  quick;  it  commences 
at  the  entrance  of  the  great  veins  into  them,  and  is  thence  propagated 
toward  the  auriculo-ventricular  opening;  but  the  last  part  which  contracts 
is  the  auricular  appendix.  The  effect  of  this  contraction  of  the  auricles  is 
to  quicken  the  flow  of  blood  from  them  into  the^ ventricles;  the  force  of 
their  contraction  not  being  sufficient  under  ordinary  circumstances  to 
cause  any  back-flow  into  the  veins.  The  reflux  of  blood  into  the  great 
veins  is,  moreover,  resisted  not  only  by  the  mass  of  blood  in  the  veins  and 
the  force  with  which  it  streams  into  the  auricles,  but  also  by  the  simulta- 
neous contraction  of  the  muscular  coats  with  which  the  large  veins  are 


112  HAND-BOOK    OF    PHYSIOLOGY. 

provided  near  their  entrance  into  the  auricles.  Any  slight  regurgitation 
from  the  right  auricle  is  limited  also  by  the  valves  at  the  junction  of  the 
subclavian  and  internal  jugular  veins,  beyond  which  the  blood  cannot 
move  backward;  and  the  coronary  vein  is  preserved  from  it  by  a  valve  at 
its  mouth. 

In  birds  and  reptiles  regurgitation  from  the  right  auricle  is  prevented 
by  valves  placed  at  the  entrance  of  the  great  veins. 

During  the  auricular  contraction  the  force  of  the  blood  propelled 
into  the  ventricle  is  transmitted  in  all  directions,  but  being  insufficient 
to  separate  the  semilunar  valves,  it  is  expended  in  distending  the  ven- 
tricle, and,  by  a  reflux  of  the  current,  in  raising  and  gradually  closing  the 
auriculo-ventricular  valves,  which,  when  the  ventricle  is  full,  form  a  com- 
plete septum  between  it  and  the  auricle. 

Action  of  the  Ventricles. — The  blood  which  is  thus  driven,  by  the 
contraction  of  the  auricles,  into  the  corresponding  ventricles,  being  added 
to  that  which  had  already  flowed  into  them  during  the  heart's  pause,  is 
sufficient  to  complete  their  diastole.  Thus  distended,  they  immediately 
contract:  so  immediately,  indeed,  that  their  systole  looks  as  if  it  were 
continuous  with  that  of  the  auricles.  The  ventricles  contract  much  more 
slowly  than  the  auricles,  and  in  their  contraction  probably  always 
thoroughly  empty  themselves,  differing  in  this  respect  from  the  auricles, 
in  which,  even  after  their  complete  contraction,  a  small  quantity  of  blood 
remains.  The  shape  of  both  ventricles  during  systole  undergoes  an  alter- 
ation, the  left  probably  not  altering  in  length  but  to  a  certain  degree  in 
breadth,  the  diameters  in  the  plane  of  the  base  being  diminished.  The 
right  ventricle  does  actually  shorten  to  a  small  extent.  The  systole  has 
the  effect  of  diminishing  the  diameter  of  the  base,  especially  in  the  plane 
of  the  auriculo-ventricular  valves;  but  the  length  of  the  heart  as  a  whole 
is  not  altered.  (Ludwig.)  During  the  systole  of  the  ventricles,  too,  the 
aorta  and  pulmonary  artery,  being  filled  with  blood  by  the  force  of  the 
ventricular  action  against  considerable  resistance,  elongate  as  well  as  ex- 
pand, and  the  whole  heart  moves  slightly  toward  the  right  and  forward, 
twisting  on  its  long  axis,  and  exposing  more  of  the  left  ventricle  ante- 
riorly than  is  usually  in  front.  When  the  systole  ends  the  heart  resumes 
its  former  position,  rotating  to  the  left  again  as  the  aorta  and  pulmonary 
artery  contract. 

Functions  of  the  Auriculo-Ventricular  Valves.— The  disten- 
sion of  the  ventricles  wiifi  blood  continues  throughout  the  whole  period 
of  their  diastole.  The  auriculo-ventricular  valves  are  gradually  brought 
into  play  by  some  of  the  blood  getting  behind  the  cusps  and  floating  them 
up;  and  by  the  time  that  the  diastole  is  complete,  the  valves  are  no  doubt 
in  apposition,  the  completion  of  this  being  brought  about  by  the  reflex 
current  caused  by  the  systole  of  the  auricles.  This  elevation  of  the  au- 


CIRCULATION    OF    THE    BLOOD.  113 

riculo-ventricnlar  valves  is,  no  doubt,  materially  aided  by  the  action  of  the 
elastic  tissue  which  has  been  shown  to  exist  so  largely  in  their  structure, 
especially  on  the  auricular  surface.  At  any  rate  at  the  commencement 
of  the  ventricular  systole  they  are  completely  closed.  It  should  be  recol- 
lected that  the  diminution  in  the  breadth  of  the  base  of  the  heart  in  its 
transverse  diameters  during  ventricular  systole  is  especially  marked  in  the 
neighborhood  of  the  auriculo- ventricular  rings,  and  thus  aids  in  render- 
ing the  auriculo-ventricular  valves  competent  to  close  the  openings,  by 
greatly  diminishing  their  diameter.  The  margins  of  the  cusps  of  the 
valves  are  still  more  secured  in  apposition  with  another,  by  the  simulta- 
neous contraction  of  the  musculi  papillares,  whose  chordae  tendineae  have  a- 
special  mode  of  attachment  for  this  object  (p.  110).  As  in  the  case  of 
the  semilunar  valves  to  be  immediately  described,  the  auriculo-ventricular 
valves  meet  not  by  their  edges  only,  but  by  the  opposed  surfaces  of  their 
thin  outer  borders.  The  semilunar  valves,  on  the  other  hand,  which  are 
closed  in  the  intervals  of  the  ventricle's  contraction  (Fig.  92,  6),  are 
forced  apart  by  the  same  pressure  that  tightens  the  auriculo-ventricular 
valves;  and,  thus,  the  whole  force  of  the  contracting  ventricles  is  directed 
to  the  expulsion  of  blood  through  the  aorta  and  pulmonary  artery. 

The  form  and  position  of  the  fleshy  columns  on  the  internal  walls  of 
the  ventricle  no  doubt  help  to  produce  this  obliteration  of  the  cavity  dur- 
ing their  contraction;  and  the  completeness  of  the  closure  may  often  be 
observed  on  making  a  transverse  section  of  a  heart  shortly  after  death,  in 
any  case  in  which  the  contraction  of  the  rigor  mortis  is  very  marked  (Fig. 
94).  In  such  a  case  only  a  central  fissure  may  be  discernible  to  the  eye 
in  the  place  of  the  cavity  of  each  ventricle. 

If  there  were  only  circular  fibres  forming  the  ventricular  wall,  it  is 
evident  that  on  systole  the  ventricle  would  elongate;  if  there  were 
only  longitudinal  fibres  the  ventricle  would  shorten  on  systole;  but  there 
are  both.  The  tendency  to  alter  in  length  is  thus  counterbalanced,  and 
the  whole  force  of  the  contraction  is  expended  in  diminishing  the  cavity 
of  the  ventricle;  or,  in  other  words,  in  expelling  its  contents. 

On  the  conclusion  of  the  systole  the  ventricular  walls  tend  to  expand 
by  virtue  of  their  elasticity,  and  a  negative  pressure  is  set  up,  which  tends 
to  suck  in  the  blood.  This  negative  or  suctional  pressure  on  the  left  side 
of  the  heart  is  of  the  highest  importance  in  helping  the  pulmonary  cir- 
culation. It  has  been  found  to  be  equal  to  23  mm.  of  mercury,  and  is 
quite  independent  of  the  aspiration  or  suction  power  of  the  thorax  in  aid- 
ing the  blood-flow  to  the  heart,  to  be  described  in  the  chapter  on  Respira- 
tion. 

Function  of  the  Musculi   Papillares. — The  special  function  of 

the  musculi  papillares  is  to  prevent  the  auriculo-ventricular  valves  from 

being  everted  into  the  auricle.     For  the  chordae  tendineae  might  allow 

the  valves  to  be  pressed  back  into  the  auricle,  were  it  not  that  when  the 

VOL.  I.— 8. 


114  HAND-BOOK    OF    PHYSIOLOGY. 

wall  of  the  ventricle  is  brought  by  its  contraction  nearer  the  auriculo- 
ventricular  orifice,  the  musculi  papillares  more  than  compensate  for  this 
by  their  own  contraction — holding  the  cords  tight,  and,  by  pulling  down 
the  valves,  adding  slightly  to  the  force  with  which  the  blood  is  expelled. 

What  has  been  said  applies  equally  to  the  auriculo-ventricular  valves 
on  both  sides  of  the  heart,  and  of  both  alike  the  closure  is  generally  com- 
plete every  time  the  ventricles  contract.  But  in  some  circumstances  the 
closure  of  the  tricuspid  valve  is  not  complete,  and  a  certain  quantity  of 
blood  is  forced  back  into  the  auricle.  This  has  been  called  the  safety- 
valve  action  of  this  valve.  The  circumstances  in  which  it  usually  happens 
^re  those  in  which  the  vessels  of  the  lung  are  already  full  enough  when 
the  right  ventricle  contracts,  as  e.g.,  in  certain  pulmonary  diseases,  in 
very  active  exertion,  and  in  great  efforts.  In  these  cases,  the  tricuspid 
valve  does  not  completely  close,  and  the  regurgitation  of  the  blood  may 
be  indicated  by  a  pulsation  in  the  jugular  veins  synchronous  with  that  in 
the  carotid  arteries. 

Function  of  the  Semilunar  Valves. — The  arterial  or  semilunar 
valves  are  forced  apart  by  the  out-streaming  blood,  with  which  the  con- 
tracting ventricle  dilates  the  large  arteries.  The  dilation  of  the  arteries 
is,  in  a  peculiar  manner,  adapted  to  bring  the  valves  into  action.  The 
lower  borders  of  the  semilunar  valves  are  attached  to  the  inner  surface  of 
a  tendinous  ring,  which  is,  as  it  were,  inlaid  at  the  orifice  of  the  artery, 
between  the  muscular  fibres  of  the  ventricle  and  the  elastic  fibres  of  the  walls 
of  the  artery.  The  tissue  of  this  ring  is  tough,  and  does  not  admit  of 
extension  under  such  pressure  as  it  is  commonly  exposed  to;  the  valves 
are  equally  inextensile,  being,  as  already  mentioned,  formed  of  tough,  close- 
textured,  fibrous  tissue,  with  strong  interwoven  cords,  and  covered  with 
endocardium.  Hence,  when  the  ventricle  propels  blood  through  the  ori- 
fice and  into  the  canal  of  the  artery,  the  lateral  pressure  which  it  exercises 
is  sufficient  to  dilate  the  walls  of  the  artery,  but  not  enough  to  stretch  in  an 
equal  degree,  if  at  all,  the  unyielding  valves  and  the  ring  to  which  their 
lower  borders  are  attached.  The  effect,  therefore,  of  each  such  propul- 
sion of  blood  from  the  ventricle  is,  that  the  wall  of  the  first  portion  of 
the  artery  is  dilated  into  three  pouches  behind  the  valves,  while  the  free 
margins  of  the  valves  are  drawn  inward  toward  its  centre  (Fig.  98,  B). 
Their  positions  may  be  explained  by  the  diagrams,  in  which  the  continu- 
ous lines  represent  a  transverse  section  of  the  arterial  walls,  the  dotted 
ones  the  edges  of  the  valves,  firstly,  when  the  valves  are  nearest  to  the 
walls  (A),  and,  secondly,  when,  the  walls  being  dilated,  the  valves  are 
drawn  away  from  them  (B). 

This  position  of  the  valves  and  arterial  walls  is  retained  so  long  as  the 
ventricle  continues  in  contraction:  but,  as  soon  as  it  relaxes,  and  the  di- 
lated arterial  walls  can  recoil  by  their  elasticity,  the  blood  is  forced  back- 
ward toward  the  ventricles  as  onward  in  the  course  of  the  circulation. 


CIRCULATION    OF    THE    BLOOD. 


115 


Part  of  the  blood  thus  forced  back  lies  in  the  pouches  (sinuses  of  Valsalva) 
(a,  Fig.  98,  B)  between  the  valves  and  the  arterial  walls;  and  the  valves 
are  by  it  pressed  together  till  their  thin  lunated  margins  meet  in  three 


FIG.  98.— Sections  of  aorta,  to  show  the  action  of  the  semilunar  valves.  A  is  intended  to  show 
the  valves,  represented  by  the  dotted  lines,  pressed  toward  the  arterial  walls,  represented  by  the  con- 
tinuous outer  line.  B  (after  Hunter)  shows  the  arterial  wall  distended  into  three  pouches  (a),  and 
drawn  away  from  the  valves,  which  are  straightened  into  the  form  of  an  equilateral  triangle,  as  rep- 
resented by  the  dotted  lines. 

lines  radiating  from  the  centre  to  the  circumference  of  the  artery  (7  and 
8,  Fig.  99). 

The  contact  of  the  valves  in  this  position,  and  the  complete  closure  of 
the  arterial  orifice,  are  secured  by  the  peculiar  construction  of  their  bor- 
ders before  mentioned.  Among  the  cords  which  are  interwoven  in  the 


FIG.  99.  —View  of  the  base  of  the  ventricular  part  of  the  heart,  showing  the  relative  position  of 
the  arterial  and  auriculo-ventricular  orifices.— %  The  muscular  fibres  of  the  ventricles  are  exposed 
by  the  removal  of  the  pericardium,  fat,  blood-vessels,  etc. ;  the  pulmonary  artery  and  aorta  have  been 
removed  by  a  section  made  immediately  beyond  the  attachment  of  the  semilunar  valves,  and  the  au- 
ricles have  been  removed  immediately  above  the  auriculo-ventricular  orifices.  The  semilunar  and 
auriculo-ventricular  valves  are  in  the  nearly  closed  condition.  1,  1,  the  base  of  the  right  ventricle; 
1'.  the  conus  arteriosus;  2, 2,  the  base  of  the  left  ventricle;  3,  3,  the  divided  wall  of  the  right  auricle; 
4,  that  of  the  left;  5,  5/  5\  the  tricuspid  valve;  6,  6',  the  mitral  valve.  In  the  angles  between  these 
segments  are  seen  the  smaller  fringes  frequently  observed;  7,  the  Interior  part  of  the  pulmonary  ar- 
tery ;  8,  placed  upon  the  posterior  part  of  the  root  of  the  aorta ;  9,  the  right,  9',  the  left  coronary  artery. 
(Allen  Thomson.) 

substance  of  the  valves,  are  two  of  greater  strength  and  prominence  than 
the  rest;  of  which  one  extends  along  the  free  border  of  each  valve,  and 
the  other  forms  a  double  curve  or  festoon  just  below  the  free  border. 


116 


HAND-BOOK    OF    PHYSIOLOGY. 


Each  of  these  cords  is  attached  by  its  outer  extremities  to  the  outer  end 
of  the  free  margin  of  its  valve,  and  in  the  middle  to  the  corpus  Arantii; 
they  thus  enclose  a  lunated  space  from  a  line  to  a  line  and  a  half  in  width, 
in  which  space  the  substance  of  the  valve  is  much  thinner  and  more  pliant 
than  elsewhere.  When  the  valves  are  pressed  down,  all  these  parts  or 
spaces  of  their  surfaces  come  into  contact,  and  the  closure  of  the  arterial 
orifice  is  thus  secured  by  the  apposition  not  of  the  mere  edges  of  the 
valves,  but  of  all  those  thin  lunated  parts  of  each  which  lie  between  the 
free  edges  and  the  cords  next  below  them.  These  parts  are  firmly  pressed 
together,  and  the  greater  the  pressure  that  falls  on  them  the  closer  and 
more  secure  is  their  apposition.  The  corpora  Arantii  meet  at  the  centre 
of  the  arterial  orifice  when  the  valves  are  down,  and  they  probably  assist 
in  the  closure;  but  they  are  not  essential  to  it,  for,  not  unfrequently, 
they  are  wanting  in  the  valves  of  the  pulmonary  artery,  which  are  then 
extended  in  larger,  thin,  flapping  margins.  In 
valves  of  this  form,  also,  the  inlaid  cords  are  less 
distinct  than  in  those  with  corpora  Arantii;  yet  the 
closure  by  contact  of  their  surfaces  is  not  less 
secure. 

It  has  been  clearly  shown  that  this  pressure  of  the 
blood  is  not  entirely  sustained  by  the  valves  alone,  but 
in  part  by  the  muscular  substance  of  the  ventricle 
(Savory).  By  making  vertical  sections  (Fig.  100) 
through  various  parts  of  the  tendinous  rings  it  is  pos- 
sible to  show  clearly  that  the  aorta  and  pulmonary 
artery,  expanding  toward  their  termination,  are  sit- 
uated upon  the  outer  edge  of  the  thick  upper  border 
of  the  ventricles,  and  that  consequently  the  portion 
of  each  semilunar  valve  adjacent  to  the  vessel  passes 
over  and  rests  upon  the  muscular  substance — being 
thus  supported,  as  it  were,  on  a  kind  of  muscular  floor 
formed  by  the  upper  border  of  the  ventricle.  The  result  of  this  arrange- 
ment is  that  the  reflux  of  the  blood  is  most  efficiently  sustained  by  the 
ventricular  wall. l 

As  soon  as  the  auricles  have  completed  their  contraction  they  begin 
again  to  dilate,  and  to  be  refilled  with  blood,  which  flows  into  them  in  a 
steady  stream  through  the  great  venous  trunks.  They  are  thus  filling 
during  all  the  time  in  which  the  ventricles  are  contracting;  and  the  con- 
traction of  the  ventricle*  being  ended,  these  also  again  dilate,  and  receive 
again  the  blood  that  flows  into  them  from  the  auricles.  By  the  time  that 
the  ventricles  are  thus  from  one-third  to  two-thirds  full,  the  auricles  are 

1  Savory's  preparations,  illustrating  this  and  other  points  in  relation  to  the  struc- 
ture and  functions  of  the  valves  of  the  heart,  are  in  the  Museum  of  St.  Bartholomew's- 
Hospital. 


FIG.  100.— Vertical  sec- 
tion through  the  aorta 
at  its  junction  with  the 
left  ventricle,  a,  Section 
of  aorta.  66,  Section  of 
two  valves,  c,  Section  of 
wall  of  ventricle,  d,  In- 
ternal surface  of  ven- 
tricle. 


CIRCULATION    OF    THE    BLOOD  117 

distended;    these,   then  suddenly  contracting,  fill  up  the  ventricles,   as 
already  described  (p.  111). 

Cardiac  .Revolution. — If  we  suppose  a  cardiac  revolution  divided 
into  five  parts,  one  of  these  will  be  occupied  by  the  contraction  of  the 
auricles,  two  by  that  of  the  ventricles,  and  two  by  repose  of  both  auricles 
and  ventricles. 

Contraction  of  Auricles   .     .     .     1  +  Repose  of  Auricles     .     .     .     4=5 
Ventricles     .     .     2  -j-       "  Ventricles      .     .     3=5 

Repose  (no  contraction  of  either 

auricles  or  ventricles)   .     .     .     2  -j-  Contraction  (of  either  auri- 
cles or  ventricles)  .     .     .     3=5 
5 

If  the  speed  of  the  heart  be  quickened,  the  time  occupied  by  each 
cardiac  revolution  is  of  course  diminished,  but  the  diminution  affects  only 
the  diastole  and  pause.  The  systole  of  the  ventricles  occupies  very  much 
the  same  time,  about  -^  sec.,  whatever  the  pulse-rate. 

The  periods  in  which  the  several  valves  of  the  heart  are  in  action  may 
be  connected  with  the  foregoing  table;  for  the  auriculo- ventricular  valves 
are  closed,  and  the  arterial  valves  are  open  during  the  whole  time  of  the 
ventricular  contraction,  while,  during  the  dilation  and  distension  of  the 
ventricles  the  latter  valves  are  shut,  the  former  open.  Thus  whenever 
the  auriculo-ventricular  valves  are  open,  the  arterial  valves  are  closed  and 
vice  versd. 


SOUNDS  OF  THE  HEAET. 

When  the  ear  is  placed  over  the  region  of  the  heart,  two  sounds  may 
be  heard  at  every  beat  of  the  heart,  which  follow  in  quick  succession, 
and  are  succeeded  by  a,  pause  or  period  of  silence.  The  first  sound  is  dull 
and  prolonged;  its  commencement  coincides  with  the  impulse  of  the 
heart,  and  just  precedes  the  pulse  at  the  wrist.  The  second  is  a  shorter 
and  sharper  sound,  with  a  somewhat  flapping  character,  and  follows  close 
after  the  arterial  pulse.  The  period  of  time  occupied  respectively  by  the 
two  sounds  taken  together,  and  by  the  pause,  are  almost  exactly  equal. 
The  relative  length  of  time  occupied  by  each  sound,  as  compared  with 
the  other,  is  a  little  uncertain.  The  difference  may  be  best  appreci- 
ated by  considering  the  different  forces  concerned  in  the  production  of 
the  two  sounds.  In  one  case  there  is  a  strong,  comparatively  slow,  con- 
traction of  a  large  mass  of  muscular  fibres,  urging  forward  a  certain 
quantity  of  fluid  against  considerable  resistance;  while  in  the  other  it  is  a 
strong  but  shorter  and  sharper  recoil  of  the  elastic  coat  of  the  large 
arteries, — shorter  because  there  is  no  resistance  to  the  flapping  back  of 


118  HAND-BOOK    OF    PHYSIOLOGY. 

the  semilunar  valves,  as  there  was  to  their  opening.  The  sounds  may 
be  expressed  by  saying  the  words  lubb — dup  (C.  J.  B.  Williams). 

The  events  which  correspond,  in  point  of  time,  with  the  first  sound, 
are  (1)  the  contraction  of  the  ventricles,  (2)  the  first  part  of  the  dilatation 
of  the  auricles,  (3)  the  closure  of  the  auriculo-ventricular  valves,  (4)  the 
opening  of  the  semilunar  valves,  and  (5)  the  propulsion  of  blood  into  the 
arteries.  The  sound  is  succeeded,  in  about  one-thirtieth  of  a  second,  by 
the  pulsation  of  the  facial  arteries,  and  in  about  one-sixth  of  a  second, 
by  the  pulsation  of  the  arteries  at  the  wrist.  The  second  sound,  in  point 
of  time,  immediately  follows  the  cessation  of  the  ventricular  contraction, 
and  corresponds  with  (a)  the  closure  of  the  semilunar  valves,  (b)  the  con- 
tinued dilatation  of  the  auricles,  (c)  the  commencing  dilatation  of  the 
ventricles,  and  (d)  the  opening  of  the  auriculo-ventricular  valves.  The 
pause  immediately  follows  the  second  sound,  and  corresponds  in  its  first 
part  with  the  completed  distension  of  the  auricles,  and  in  its  second 
with  their  contraction,  and  the  completed  distension  of  the  ventricles; 
the  auriculo-ventricular  valves  being,  all  the  time  of  the  pause,  open,  and 
the  arterial  valves  closed. 

Causes. — The  chief  cause  of  the  first  sound  of  the  heart  appears  to 
be  the  vibration  of  the  auriculo-ventricular  valves,  due  to  their  stretch- 
ing, and  also,  but  to  a  less  extent,  of  the  ventricular  walls,  and  coats  of 
the  aorta  and  pulmonary  artery,  all  of  which  parts  are  suddenly  put  into 
a  state  of  tension  at  the  moment  of  ventricular  contraction.  The  effect 
may  be  intensified  by  the  muscular  sound  produced  by  contraction  of  the 
mass  of  muscular  fibres  which  form  the  ventricle. 

The  cause  of  the  second  sound  is  more  simple  than  that  of  the  first. 
It  is  probably  due  entirely  to  the  sudden  closure  and  consequent  vibration 
of  the  semilunar  valves  when  they  are  pressed  down  across  the  orifices  of 
the  aorta  and  pulmonary  artery.  The  influence  of  the  valves  in  produc- 
ing the  sound  is  illustrated  by  the  experiment  performed  on  large  ani- 
mals, such  as  calves,  in  which  the  results  could  be  fully  appreciated.  In 
these  experiments  two  delicate  curved  needles  were  inserted,  one  into  the 
aorta,  and  another  into  the  pulmonary  artery,  below  the  line  of  attach- 
ment of  the  semilunar  valves,  and,  after  being  carried  upward  about  half 
an  inch,  were  brought  out  again  through  the  coats  of  the  respective  vessels, 
so  that  in  each  vessel  one  valve  was  included  between  the  arterial  walls 
and  the  wire.  Upon  applying  the  stethoscope  to  the  vessels,  after  such 
an  operation,  the  second  sound  had  ceased  to  be  audible.  Disease  of 
these  valves^  when  so  extensive  as  to  interfere  with  their  efficient  action, 
also  often  demonstrates  the  same  fact  by  modifying  or  destroying  the 
distinctness  of  the  second  sound. 

One  reason  for  the  second  sound  being  a  clearer  and  sharper  one  than 
the  first  may  be,  that  the  semilunar  valves  are  not  covered  in  by  the  thick 
layer  of  fibres  composing  the  walls  of  the  heart  to  such  an  extent  as  are 


CIRCULATION    OF    THE    BLOOD.  119 

the  auriculo-vcntricidar.  It  might  be  expected  therefore  that  their  vibra- 
tion would  be  more  easily  heard  through  a  stethoscope  applied  to  the 
walls  of  the  chest. 

The  contraction  of  the  auricles  which  takes  place  in  the  end  of  the 
pause  is  inaudible  outside  the  chest,  but  may  be  heard,  when  the  heart 
is  exposed  and  the  stethoscope  placed  on  it,  as  a  slight  sound  preceding 
and  continued  into  the  louder  sound  of  the  ventricular  contraction. 

The  Impulse  of  the  Heart. — At  the  commencement  of  each  ven- 
tricular contraction,  the  heart  may  be  felt  to  beat  with  a  slight  shock  or 
impulse  against  the  walls  of  the  chest.  The  force  of  the  impulse,  and  the 
extent  to  which  it  may  be  perceived  beyond  this  point,  vary  considerably 
in  different  individuals,  and  in  the  same  individual  under  different  cir- 
cumstances. It  is  felt  more  distinctly,  and  over  a  larger  extent  of  surface, 
in  emaciated  than  in  fat  and  robust  persons,  and  more  during  a  forced  ex- 
piration than  in  a  deep  inspiration;  for,  in  the  one  case,  the  intervention 
of  a  thick  layer  of  fat  or  muscle  between  the  heart  and  the  surface  of  the 
chest,  and  in  the  other  the  inflation  of  the  portion  of  lung  which  overlaps 
the  heart,  prevents  the  impulse  from  being  fully  transmitted  to  the  sur- 
face. An  excited  action  of  the  heart,  and  especially  a  hypertrophied  con- 
dition of  the  ventricles,  will  increase  the  impulse;  while  a  depressed  con- 
dition, or  an  atrophied  state  of  the  ventricular  walls,  will  diminish  it. 

Cause  of  the  Impulse. — During  the  period  which  precedes  the 
ventricular  systole,  the  apex  of  the  heart  is  situated  upon  the  diaphragm 
and  against  the  chest-wall  in  the  fifth  intercostal  space.  When  the  ven- 
tricles contract,  their  walls  become  hard  and  tense,  since  to  expel  their 
contents  into  the  arteries  is  a  distinctly  laborious  action,  as  it  is  resisted 
by  the  tension  within  the  vessels.  It  is  to  this  sudden  hardening  that  the 
impulse  of  the  heart  against  the  chest-wall  is  due,  and  the  shock  of  the 
sudden  tension  may  be  felt  not  only  externally,  but  also  internally,  if  the 
abdomen  of  an  animal  be  opened  and  the  finger  be  placed  upon  the  under 
surface  of  the  diaphragm,  at  a  point  corresponding  to  the  under  surface 
of  the  ventricle.  The  shock  is  felt,  and  possibly  seen  more  distinctly, 
because  of  the  partial  rotation  of  the  heart,  already  spoken  of,  along  its 
long  axis  toward  the  right.  The  movement  produced  by  the  ventricular 
contraction  may  be  registered  by  means  of  an  instrument  called  the  cardio- 
graph, and  it  will  be  found  to  correspond  almost  exactly  with  a  tracing 
obtained  by  the  same  instrument  applied  over  the  contracting  ventricle 
itself. 

The  Cardiograph  (Fig.  101)  consists  of  a  cup-shaped  metal  box,  over 
the  open  front  of  which  is  stretched  an  elastic  membrane,  upon  which  is 
fixed  a  small  knob  of  hard  wood  or  ivory.  This  knob,  however,  may  be 
attached  instead,  as  in  the  figure,  to  the  side  of  the  box  by  means  of  a 
spring,  and  may  be  made  to  act  upon  a  metal  disc  attached  to  the  elastic 
membrane. 


120 


HAND-BOOK    OF    PHYSIOLOGY. 


The  knob  (A)  is  for  application  to  the  chest-wall  over  the  place  of  the 
greatest  impulse  of  the  heart.     The  box  or  tympanum  communicates  by 

means  of  an  air-tight  elastic  tube  (/)  with  the 
interior  of  a  second  tympanum  (Fig.  102,  l>),  in 
connection  with  which  is  a  long  and  light  lever 
(a).  The  shock  of  the  heart's  impulse  being 
communicated  to  the  ivory  knob,  and  through 
it  to  the  first  tympanum,  the  effect  is,  of  course, 
at  once  transmitted  by  the  column  of  air  in 
the  elastic  tube  to  the  interior  of  the  second 
tympanum,  also  closed,  and  through  the  elastic 
and  movable  lid  of  the  latter  to  the  lever,  which 
is  placed  in  connection  with  a  registering  appa- 
101.  ratus,  which  consists  generally  of  a  cylinder  or 

drum    covered  with   smoked  paper,  revolving 

according  to  a  definite  velocity  by  clockwork.     The  point  of  the  lever 

writes  upon  the  paper,  and  a  tracing  of  the  heart's  impulse  is  thus  obtained. 

By  placing  three  small  india-rubber  air  -bags  in  the  interior  respec- 


FIG.  102.—  Marey 's  Tambour  ( b ),  to  which  the  movement  of  the  column  of  air  in  the  first  tym- 
panum is  conducted  by  the  tube,/,  and  from  which  it  is  communicated  by  the  lever,  o,  to  a  revolving 
cylinder,  so  that  the  tracing  of  the  movement  of  the  impulse  beat  is  obtained. 

tively  of  the  right  auricle,  the  right  ventricle,  and  in  an  intercostal  space 
in  front  of  the  heart  of  living  animals  (horse),  and  placing  these  bags,  by 
means  of  long  narrow  tubes,  in  communication  with  three  levers,  arranged 


FIG.  103.— Tracing  of  the  impulse  of  the  heart  of  man.    (Marey.) 

one  over  the  other  in  connection  with  a  registering  apparatus  (Fig.  104), 
MM.  Chauveau  and  Marey  have  been  able  to  measure  with  much  accuracy 
the  variations  of  the  endocardial  pressure  and  the  comparative  duration 


CIRCULATION    OF    THE    BLOOD. 


121 


of  the  contractions  of  the  auricles  and  ventricles.  By  means  of  the  same 
apparatus,  the  synchronism  of  the  impulse  with  the  contraction  of  the 
ventricles,  is  also  well  shown;  and  the  causes  of  the  several  vibrations  of 
which  it  is  really  composed,  have  been  discovered. 

In  the  tracing  (Fig  105),  the  intervals  between  the  vertical  lines  rep- 
resent periods  of  a  tenth  of  a  second.     The  parts   on  which  any  given 


FIG.  104. — Apparatus  of  MM.  Chauveau  and  Marey  for  estimating  the  variations  of  endocardia! 
pressure,  and  production  of  impulse  of  the  heart. 

vertical  line  falls  represent,  of  course,  simultaneous  events.  Thus, — it 
will  be  seen  that  the  contraction  of  the  auricle,  indicated  by  the  upheaval 
of  the  tracing  at  A  in  first  tracing,  causes  a  slight  increase  of  pressure  in 
the  ventricle  (A'  in  second  tracing),  and  produces  a  tiny  impulse  (A"  in 
third  tracing).  So  also,  the  closure  of  the 
semilunar  valves,  while  it  causes  a  momen- 
tarily increased  pressure  in  the  ventricle  at  D', 
does  not  fail  to  affect  the  pressure  in  the  auri- 
cle D",  and  to  leave  its  mark  in  the  tracing  of 
the  impulse  also,  D", 

The  large  upheaval  of  the  ventricular  and 
the  impulse  tracings,  between  A'  and  D',  and 
A"  and  D",  are  caused  by  the  ventricular  con- 
traction, while  the  smaller  undulatitfns,  between 
B  and  c,  B'  and  c',  B"  and  c",  are  caused  by 
the  vibrations  consequent  on  the  tightening 
and  closure  of  the  auriculo- ventricular  valves. 

Although,  no  doubt,  the  method  thus  de- 

.,      ,  ,  •      ,  i  -      impulse  of  the  heart,  to  be  read 

Scribed  may  show  a  perfectly  Correct  View  of  from  left  to  rieht,  obtained  by 
, i  ,  , .  .  , .  .,11-iT  Chauveau  and  Marey's  apparatus. 

the  endocardiac  pressure  variations,  it  should  be 

recollected  that  the  muscular  walls  may  grip  the  air-bags,  even  after  the 
complete  expulsion  of  the  contents  of  the  chamber,  and  so  the  lever  might 
remain  for  a  too  long  time  in  the  position  of  extreme  tension,  and  would 


FIG.  105.— Tracings  of  (1),  In- 
fra-auricular, and  ( 2 ),  Intra-ven- 
tricular  pressures,  and  ( 3 ),  of  the 


122  HAND-BOOK    OF    PHYSIOLOGY 

represent  on  the  tracing  not  only,  as  it  ought  to  do,  the  auricular  or 
ventricular  pressure  on  the  blood,  but,  also  afterward,  the  muscular  pres- 
sure exerted  upon  the  bags  themselves.  (M.  Foster.) 

FREQUENCY  AND  FORCE  OF  THE  HEART'S  ACTION. 

The  heart  of  a  healthy  adult  iran  contracts  from  seventy  to  seventy-five 
times  in  a  minute;  but  many  circumstances  cause  this  rate,  which  of 
course  corresponds  with  that  of  the  arterial  pulse,  to  vary  even  in  health. 
The  chief  are  age,  temperament,  sex,  food  and  drink,  exercise,  time  of 
day,  posture,  atmospheric  pressure,  temperature. 

Age. — The  frequency  of  the  heart's  action  gradually  diminishes  from 
the  commencement  to  near  the  end  of  life,  but  is  said  to  rise  again 
somewhat  in  extreme  old  age,  thus: — 

Before  birth  the  average  number  of  pulses  in  a  minute  is  150 

Just  after  birth        .         .         .         .         .  from  140  to  130 

During  the  first  year                 .         .         .  "     130  "  115 

During  the  second  year  "    115  t(  100 

During  the  third  year  "     100  "     90 

About  the  seventh  year   .         .         .         .  "       90  "     85 
About  the  fourteenth  year,  the  average 

number  of  pulses  in  a  minute  is  "      85  "     80 

In  adult  age "      80  "     70 

In  old  age "      70  "     60 

In  decrepitude "      75  "     65 

Temperament  and  Sex. — In  persons  of  sanguine  temperament,  the 
heart  acts  somewhat  more  frequently  than  in  those  of  the  phlegmatic; 
and  in  the  female  sex  more  frequently  than  in  the  male. 

Food  and  Drink.  Exercise. — After  a  meal  its  action  is  accelerated, 
and  still  more  so  during  bodily  exertion  or  mental  excitement;  it  is  slower 
during  sleep. 

Diurnal  Variation. — It  appears  that,  in  the  state  of  health,  the  pulse 
is  most  frequent  in  the  morning,  and  becomes  gradually  slower  as  the  day 
advances,  and  that  this  diminution  of  frequency  is  both  more  regular 
and  more  rapid  in  the  evening  than  in  the  morning. 

Posture. — It  is  found  that,  as  a  general  rule,  the  pulse,  especially  in 
the  adult  male,  is  more  frequent  in  the  standing  than  in  the  sitting  pos- 
ture, and  in  the  latter  than  in  the  recumbent  position;  the  difference 
being  greatest  between  the  standing  and  the  sitting  posture.  The  effect 
of  change  of  posture  is  greater  as  the  frequency  of  the  pulse  is  greater, 
and,  accordingly,  is  more  marked  in  the  morning  than  in  the  evening. 
By  supporting  the  body  in  different  postures,  without  the  aid  of  mus- 
cular effort  of  the  individual,  it  has  been  proved  that  the  increased  fre- 
quency of  the  pulse  in  the  sitting  and  standing  positions  is  dependent 
upon  the  muscular  exertion  engaged  in  maintaining  them;  the  usual 
effect  of  these  postures  on  the  pulse  being  almost  entirely  prevented  when 
the  usually  attendant  muscular  exertion  was  rendered  unnecessary.  (Guy.) 


CIRCULATION    OF    THE    BLOOD. 


123 


Atmospheric  Pressure. — The  frequency  of  the  pulse  increases  in  a 
corresponding  ratio  with  the  elevation  above  the  sea. 

Temperature. — The  rapidity  and  force  of  the  heart's  contractions  are 
largely  influenced  by  variations  of  temperature.  The  frog's  heart,  when 
excised,  ceases  to  beat  if  the  temperature  be  reduced  to  32°  F.  (0°  C.). 
When  heat  is  gradually  applied  to  it,  both  the  speed  and  force  of  the 
heart's  contractions  increase  till  they  reach  a  maximum.  If  the  tem- 
perature is  still  further  raised,  the  beats  become  irregular  and  feeble,  and 
the  heart  at  length  stands  still  in  a  condition  of  "heat-rigor." 

Similar  effects  are  produced  in  warm-blooded  animals.  In  the  rabbit, 
the  number  of  heart -beats  is  more  than  doubled  when  the  temperature  of 
the  air  was  maintained  at  105°  F.  (40°.5  C.).  At  113°— 114°  F.  (45°  C.), 
the  rabbit's  heart  ceases  to  beat. 


Relative  Frequency  of  the  Pulse  to  that  of  Respiration. — 

In  health  there  is  observed  a  nearly  uniform  relation  between  the  fre- 
quency of  the  pulse  and  of  the  respirations;  the  proportion  being,  on  an 
average,  one  respiration  to  three  or  four  beats  of  the  heart.  The  same 
relation  is  generally  maintained  in  the  cases  in  which  the  pulse  is  naturally 
accelerated,  as  after  food  or  exercise;  but  in  disease  this  relation  usually 
ceases.  In  many  affections  accompanied  with  increased  frequency  of  the 
pulse,  the  respiration  is,  indeed,  also  accelerated,  yet  the  degree  of  its 
acceleration  may  bear  no  definite  proportion  to  the  increased  number  of 
the  heart's  actions:  and  in  many  other  cases,  the  pulse  becomes  more  fre- 
quent without  any  accompanying  increase  in  the  number  of  respirations; 
or,  the  respiration  alone  may  be  accelerated,  the  number  of  pulsations  re- 
maining stationary,  or  even  falling  below  the  ordinary  standard. 

The  Force  of  the  Ventricular  Systole  and  Diastole.— The 
force  of  the  left  ventricular  systole  is  more  than  double  that  exerted  by  the 
contraction  of  the  right:  this  difference  in  the  amount  of  force  exerted 
by  the  contraction  of  the  two  ventricles,  results  from  the  walls  of  the  left 
ventricle  being  about  twice  or  three  times  as  thick  as  those  of  the  right. 
And  the  difference  is  adapted  to  the  greater  degree  of  resistance  which  the 
left  ventricle  has  to  overcome,  compared  with  that  to  be  overcome  by  the 
right:  the  former  having  to  propel  blood  through  every  part  of  the  body, 
the  latter  only  through  the  lungs. 

The  actual  amount  of  the  intra- ventricular  pressures  during  systole 
in  the  dog  has  been  found  to  be  2*4  inches  (60  mm.)  of  mercury  in  the 
right  ventricle,  and  6  inches  (150  mm.)  in  the  left.  During  diastole  there 
is  in  the  right  ventricle  a  negative  or  suction  pressure  of  about  |  of  an 
inch  (  —  17  to  —16  mm.),  and  in  the  left  ventricle  from  2  inches  to  $•  of 
an  inch  ( — 52  to  — 20  mm.).  Part  of  this  fall  in  pressure,  and  possibly 
the  greater  part,  is  to  be  referred  to  the  influence  of  respiration;  but  with- 
out this  the  negative  pressure  of  the  left  ventricle  caused  by  its  active 
dilatation  is  about  |  of  an  inch  (23  mm.)  of  mercury. 

The  right  ventricle  is  undoubtedly  aided  by  this  suction  power  of  the 


124  HAND-BOOK    OF    PHYSIOLOGY. 

left,  so  that  the  whole  of  the  work  of  conducting  the  pulmonary  circula- 
tion does  not  fall  upon  the  right  side  of  the  heart,  but  is  assisted  by  the 
left  side. 

The  Force  of  the  Auricular  Systole  and  Diastole. — The 
maximum  pressure  within  the  right  auricle  is  about  \  of  an  inch  (20  mm.) 
of  mercury,  and  is  probably  somewhat  less  in  the  left.  It  has  been  found 
that  during  diastole  the  pressure  within  both  auricles  sinks  considerably 
below  that  of  the  atmosphere;  and  as  some  fall  in  pressure  takes  place, 
even  when  the  thorax  of  the  animal  operated  upon  has  been  opened,  a 
certain  proportion  of  the  fall  must  be  due  to  active  auricular  dilatation 
independent  of  respiration.  In  the  right  auricle,  this  negative  pressure 
is  about  —10  mm. 

Work  Done  by  the  Heart. — In  estimating  the  work  done  by  any 
machine  it  is  usual  to  express  it  in  terms  of  the  "unit  of  work."  The  unit 
of  work  is  defined  to  be  the  energy  expended  in  raising  a  unit  of  weight 
(1  Ib.)  through  a  unit  of  height  (1  ft.).  In  England,  the  unit  of  work 
is  the  "foot-pound,"  in  France,  the  "kilogrammetre." 

The  work  done  by  the  heart  at  each  contraction  can  be  readily  found 
by  multiplying  the  weight  of  blood  expelled  by  the  ventricles  by  the 
height  to  which  the  blood  rises  in  a  tube  tied  into  an  artery.  This  height 
was  found  to  be  about  9  ft.  in  the  horse,  and  the  estimate  is  nearly  correct 
for  a  large  artery  in  man.  Taking  the  weight  of  blood  expelled  from  the 
left  ventricle  at  each  systole  as  6  oz.,  i.e.,  f  Ib.,  we  have  9  x  f  =  3 -375 
foot-pounds  as  the  work  done  by  the  left  ventricle  at  each  systole;  and 
adding  to  this  the  work  done  by  the  right  ventricle  (about  one-third  that 
of  the  left)  we  have  3*375  X  1*125  =  4*5  foot-pounds  as  the  work  done 
by  the  heart  at  each  eontraction.  Other  estimates  give  \  kilogrammetre, 
or  about  3-J-  foot-pounds.  Haughton  estimates  the  total  work  of  the  heart 
in  24  hours  as  about  124  foot-tons. 

Influence  of  the  Nervous  System  on  the  Action  of  the 
Heart. — The  hearts  of  warm-blooded  animals  cease  to  beat  almost  if  not 
quite  immediately  after  removal  from  the  body,  and  are,  therefore,  un- 
favorable for  the  study  of  the  nervous  mechanism  which  regulates  their 
action.  Observations  have  hitherto,  therefore,  been  principally  directed 
to  the  heart  of  cold-blooded  animals,  e.g.,  the  frog,  tortoise,  and  snake, 
which  will  continue  to  beat  under  favorable  conditions  for  many  hours 
after  removal  from  the  body.  Of  these  animals,  the  frog  is  the  one  mostly 
employed,  and,  indeed,  until  recently,  it  was  from  the  study  of  the  frog's 
heart  that  the  chief  part  of  our  information  was  obtained.  If  removed 
from  the  body  entire,  the  frog's  heart  will  continue  to  beat  for  many  hours 
and  even  days,  and  the  beat  has  no  apparent  difference  from  the  beat  of 
the  heart  before  removal  from  the  body;  it  will  take  place  without  the 
presence  of  blood  or  other  fluid  within  its  chambers.  If  the  beats  have 
"become  infrequent,  an  additional  beat  may  be  induced  by  stimulating 


CIRCULATION    OF    THE    BLOOD. 


125 


the  heart  by  means  of  a  blunt  needle;  but  the  time  before  the  stimulus 
applied  produces  its  result  (the  latent  period)  is  very  prolonged,  and  as 
in  this  way  the  cardiac  beat  is  like  the  contraction  of  unstriped  muscle, 
the  method  has  been  likened  to  a  peristaltic  contraction. 

There  is  much  uncertainty  about  the  nervous  mechanism  of  the  beat 
of  the  frog's  heart,  but  what  has  just  been  said  shows,  at  any  rate,  two 
things;  firstly,  that  as  the  heart  will  beat  when  removed  from  the  body  in 
a  way  differing  not  at  all  from  the  normal,  it  must  contain  within  itself  the 
mechanism  of  rhythmical  contraction;  and  secondly,  that  as  it  can  beat 
without  the  presence  of  fluid  within  its  chambers,  the  movement  cannot 
depend  merely  on  reflex  excitation  by  the  entrance  of  blood.  The  nervous 
apparatus  existing  in  the  heart  itself  consists  of  collections  of  microscopic 
ganglia,  and  of  nerve- fibres  proceeding  from  them.  These  ganglia  are 


-AA     AA 


FIG.  106.— Heart  of  frog.  (Burdon-Sanderson  after  Fritsche.)  Front  view  to  the  left,  back  view 
to  the  right.  A  A.  Aortae.  V.  cs.  Venae  cavae  superiores.  At  s,  left  auricle.  At  d,  right  auricle. 
Fen.,  ventricle.  B.  ar.,  Bulbus  arteriosus.  S.  v.,  Sinus  venosus.  V.  c.  i.,  Vena  cava  inferior.  V. 
ft .,  Venae  hepaticae .  V .  p . ,  Venae  pulmonales . 

demonstrable  as  being  collected  chiefly  into  three  groups;  one  is  in  the 
wall  of  the  sinus  venosus  (Remakes);  a  second,  near  the  junction  between 
the  auricle  and  ventricle  (Bidder's);  and  the  third  in  the  septum  between 
the  auricles. 

Some  very  important  experiments  seem  to  identify  the  rhythmical 
contractions  of  the  frog's  heart  with  these  ganglia.  If  the  heart  be  re- 
moved entire  from  the  body,  the  sequence  of  the  contraction  of  its  several 
beats  will  take  place  with  rhythmical  regularity,  viz.,  of  the  sinus  veno- 
sus, the  auricles,  the  ventricle,  and  bulbus  arteriosus,  in  order.  If  the 
heart  be  removed  at  the  junction  of  the  sinus  and  auricle,  the  former  will 
continue  to  beat,  but  the  removed  portion  will  for  a  short  variable  time 
stop  beating,  and  then  resume  its  beats,  but  with  a  rhythm  different  to 
that  of  the  sinus:  and,  further,  if  the  ventricle  be  removed,  it  will  take 
a  still  longer  time  before  recommencing  its  pulsation  after  its  removal 
than  the  larger  portion  consisting  of  the  auricles  and  ventricle,  and  its 
rhythm  is  different  from  that  of  the  unremoved  portion,  and  not  so  regu- 
lar, nor  will  it  continue  to  pulsate  so  long:  during  the  period  of  stop- 
page a  contraction  will  occur  if  the  ventricle  be  mechanically  or  otherwise 
stimulated.  If  the  lower  two-thirds  or  apex  of  the  ventricle  be  removed, 
the  remainder  of  the  heart  will  go  on  beating  regularly  in  the  body,  but 


126  HAND-BOOK    OF    PHYSIOLOGY. 

this  part  will  remain  motionless,  and  will  not  beat  spontaneously,  although 
it  will  respond  to  stimuli.  If  the  heart  be  divided  lengthwise,  its  parts 
will  continue  to  pulsate  rhythmically,  and  the  auricles  may  be  cut  up  into 
pieces,  and  the  pieces  will  continue  their  movements  of  contraction.  It 
will  be  thus  seen  that  the  rhythmical  movements  appear  to  be  more  marked 
in  the  parts  supplied  by  the  ganglia,  and  that  the  apical  portion  of  the 
ventricle,  in  which  the  ganglia  are  not  found,  does  not  possess  the  power 
of  automatic  movement.  Although  the  theory  that  the  pulsations  of  the 
rest  of  the  heart  are  dependent  upon  that  of  the  sinus,  and  to  stimuli  pro- 
ceeding from  it,  when  connection  is  maintained,  and  only  to  reflex  stim- 
uli when  removal  has  taken  place,  cannot  be  absolutely  upheld,  yet  it  is 
evident  that  the  power  of  spontaneous  contraction  is  strongest  in  the 
sinus,  less  strong  in  the  auricles,  and  less  so  still  in  the  ventricle,  and 
that,  therefore,  the  sinus  ganglia  are  probably  important  in  exciting  the 
rhythmical  contraction  of  the  whole  heart.  This  is  expressed  in  the  fol- 
lowing way: — "The  power  of  independent  rhythmical  contraction  de- 
creases regularly  as  we  pass  from  the  sinus  to  the  ventricles,"  and  "The 
rhythmical  power  of  each  segment  of  the  heart  varies  inversely  as  its  dis- 
tance from  the  sinus."  (Gaskell.) 

It  has  been  recently  shown  that,  under  appropriate  stimuli,  even  the 
extreme  apex  of  the  ventricle  in  the  tortoise  may  take  on  rhythmical 
contractions,  or  in  other  words  may  be  "taught  to  beat"  rhythmically. 
(Gaskell.) 

Inhibition  of  the  Heart's  Action. — Although,  under  ordinary 
conditions,  the  apparatus  of  ganglia  and  nerve-fibres  in  the  substance 
of  the  heart  forms  the  medium  through  which  its  action  is  excited  and 
rhythmically  maintained,  yet  they,  and,  through  them,  the  heart's  con- 
tractions, are  regulated  by  nerves  which  pass  to  them  from  the  higher 
nerve-centres.  These  nerves  are  branches  from  the  pneumogastric  or 
vagus  and  the  sympathetic. 

The  influence  of  the  vagi  nerves  over  the  heart-beat  may  be  shown  by 
stimulating  one  (especially  the  right)  or  both  of  the  nerves  when  a  record 
is  being  taken  of  the  beats  of  the  frog's  heart.  If  a  single  induction  shock 
be  sent  into  the  nerve,  the  heart,  after  a  short  interval,  ceases  beating, 
but  after  the  suppression  of  several  beats  resumes  its  action.  As  already 
mentioned,  the  effect  of  the  stimulus  is  not  immediately  seen,  and  one  beat 
may  occur  before  the  heart  stops  after  the  application  of  the  electric-cur- 
rent. The  stoppage  of  the  heart  may  occur  apparently  in  one  of  two 
ways,  either  by  diminution  of  the  strength  of  the  systole  or  by  increas- 
ing the  length  of  the  diastole.  The  stoppage  of  the  heart  may  be  brought 
about  by  the  application  of  the  electrodes  to  any  part  of  the  vagus,  but 
most  effectually  if  they  are  applied  near  the  position  of  Remak's  ganglia. 
It  is  supposed  that  the  fibres  of  the  vagi,  therefore,  terminate  there  in 


CIRCULATION    OF    THE    BLOOD.  127 

inhibitory  ganglia  in  the  heart-walls,  and  that  the  inhibition  of  the  heart's 
lii'iits  bv  means  of  the  vagus,  is  not  a  simple  action,  but  that  it  is  pro- 
duced by  stimulating  centres  in  the  heart  itself.  These  inhibitory  centres 
are  paralyzed*  by  atropin,  and  then  no  amount  of  stimulation  of  the  vagus, 
or  of  the  heart  itself,  will  produce  any  effect  upon  the  cardiac  beats. 
"Urari  in  large  doses  paralyzes  the  vagus  fibres,  but  in  this  case,  as  the 
inhibitory  action  can  be  produced  by  direct  stimulation  of  the  heart,  it  is 
inferred  that  this  drug  does  not  paralyze  the  ganglia  themselves.  Mus- 
carin  and  pilocarpin  appear  to  produce  effects  similar  to  those  obtained 
by  stimulating  the  vagus  fibres. 

If  a  ligature  be  tightly  tied  round  the  heart  over  the  situation  of  the 
ganglia  between  the  sinus  and  the  auricles,  the  heart  stops  beating. 
This  experiment  (Stannius')  would  seem  to  stimulate  the  inhibitory  gan- 
glia, but  for  the  remarkable  fact  that  atropin  does  not  interfere  with  its 
success.  If  the  part  (the  ventricle)  below  the  ligature  be  cut  off,  it  will 
begin  and  continue  to  beat  rhythmically,  this  may  be  explained  by  sup- 
posing that  the  stimulus  of  section  induces  pulsation  in  the  part  which 
is  removed  from  the  influence  of  the  inhibitory  ganglia.  ' 

So  far,  the  effect  of  the  terminal  apparatus  of  the  vagi  has  been  con- 
sidered; there  is,  however,  reason  for  believing  that  the  vagi  nerves  are 
simply  the  media  of  an  inhibitory  or  restraining  influence  over  the  action 
of  the  heart,  which  is  conveyed  through  them  from  a  centre  in  the  me- 
dulla oblongata  which  is  always  in  operation,  and,  because  of  its  restrain- 
ing the  heart's  action,  is  called  the  car dio -inhibitory  centre.  For,  on 
dividing  these  nerves,  the  pulsations  of  the  heart  are  increased  in  fre- 
quency, an  effect  opposite  to  that  produced  by  stimulation  of  their 
divided  (peripheral)  ends.  The  restraining  influence  of  the  centre  in  the 
medulla  may  be  increased  reflexly,  producing  slowing  or  stoppage  of  the 
heart,  through  influence  passing  from  it  down  the  vagi.  As  an  example 
of  the  latter,  the  well-known  effect  on  the  heart  of  a  violent  blow  on  the 
epigastrium  may  be  referred  to.  The  stoppage  of  the  heart's  action  is  due 
to  the  conveyance  of  the  stimulus  by  fibres  of  the  sympathetic  to  the 
medulla  oblongata,  and  its  subsequent  reflection  through  the  vagi  to  the 
inhibitory  ganglia  of  the  heart.  It  is  also  believed  that  the  power  of  the 
medullary  inhibitory  centre  may  be  reflexly  lessened,  producing  acceler- 
ated action  of  the  heart. 

Acceleration  of  Heart's  Action.— Through  certain  fibres  of  the 
sympathetic,  the  heart  receives  an  accelerating  influence  from  the  medulla 
oblongata.  These  accelerating  nerve-fibres,  issuing  from  the  spinal  cord 
in  the  neck,  reach  the  inferior  cervical  ganglion,  and  pass  thence  to  the 
cardiac  plexus,  and  so  to  the  heart.  Their  function  is  shown  in  the 
quickened  pulsation  which  follows  stimulation  of  the  spinal  cord,  when 
the  latter  has  been  cut  off  from  all  connection  with  the  heart,  excepting 
that  which  is  formed  by  the  accelerating  filaments  from  the  inferior  cer- 


128  HAND-BOOK    OF    PHYSIOLOGY. 

vical  ganglion.  Unlike  the  inhibitory  fibres  of  the  pneumogastric,  the 
accelerating  fibres  are  not  continuously  in  action. 

The  accelerator  nerves  must  not,  however,  be  considered  as  direct 
antagonists  of  the  vagus;  for  if  at  the  moment  of  their  maximum  stimu- 
lation, the  vagus  be  stimulated  with  minimum  currents,  inhibition  is 
produced  with  the  same  readiness  as  if  these  were  not  acting. 

The  connection  of  the  heart  with  other  organs  by  means  of  the  nerv- 
ous system,  and  the  influences  to  which  it  is  subject  through  them,  are 
shown  in  a  striking  manner  by  the  phenomena  of  disease.  The  influence 
of  mental  shock  in  arresting  or  modifying  the  action  of  the  heart,  the 
slow  pulsation  which  accompanies  compression  of  the  brain,  the  irregu- 
larities and  palpitations  caused  by  dyspepsia  or  hysteria,  are  good  evidence 
of  the  connection  of  the  heart  with  other  organs  through  the  nervous 
system. 

The  action  of  the  heart  is  no  doubt  also  very  materially  affected  by 
the  nutrition  of  its  walls  by  a  sufficient  supply  of  healthy  blood  sent  to 
them,  and  it  is  not  unlikely  that  the  apparently  contradictory  effect  of 
poisons  may  be  explained  by  supposing  that  the  influence  of  some  of  them 
is  either  partially  or  entirely  directed  to  the  muscular  tissue  itself,  and 
not  to  the  nervous  apparatus  alone.  As  will  be  explained  presently,  the 
heart  exercises  a  considerable  influence  upon  the  condition  of  the  pressure 
of  blood  within  the  arteries,  but  in  its  turn  the  blood-pressure  within  the 
arteries  reacts  upon  the  heart,  and  has  a  distinct  effect  upon  its  contrac- 
tions, increasing  by  its  increase,  and  vice  versd,  the  force  of  the  cardiac 
beat,  although  the  frequency  is  diminished  as  the  blood-pressure  rises. 
The  quantity  (and  quality?)  of  the  blood  contained  in  each  chamber,  too, 
has  an  influence  upon  its  systole,  and  within  normal  limits  the  larger  the 
quantity  the  stronger  the  contraction.  Kapidity  of  systole  does  not  of 
necessity  indicate  strength,  as  two  weak  contractions  often  do  no  more 
work  than  one  strong  and  prolonged.  In  order  that  the  heart  may  do  its 
maximum  work,  it  must  be  allowed  free  space  to  act;  for  if  obstructed, 
in  its  action  by  mechanical  outside  pressure,  as  by  an  excess  of  fluid  within 
the  pericardium,  such  as  is  produced  by  inflammation,  or  by  an  over- 
loaded stomach,  or  what  not,  the  pulsations  become  irregular  and  feeble. 

THE  AKTEKIES. 

Distribution. — The  arterial  system  begins  at  the  left  ventricle  in  a 
single  large  trunk,  the  aorta,  which  almost  immediately  after  its  origin 
gives  off  in  its  course  in  the  thorax  three  large  branches  for  the  supply 
of  the  head,  neck,  and  upper  extremities;  it  then  traverses  the  thorax 
and  abdomen,  giving  off  branches,  some  large  and  some  small,  for  the 
supply  of  the  various  organs  and  tissues  it  passes  on  its  way.  In  the 
abdomen  it  divides  into  two  chief  branches,  for  the  supply  of  the  lower 


CIRCULATION    OF    THE    BLOOD. 


129 


extremities.  The  arterial  branches  wherever  given  off  divide  and  sub- 
divide, until  the  calibre  of  each  subdivision  becomes  very  minute,  and 
these  minute  vessels  pass  into  capillaries.  Arteries  are,  as  a  rule,  placed 
in  situations  v  protected  from  pressure  and  other  dangers,  and  are,  with 
few  exceptions,  straight  in  their  course,  and  frequently  communicate  with 
other  arteries  (anastomose  or  inosculate).  The  branches  are  usually 
given  off  at  an  acute  angle,  and  the  area  of  the  branches  of  an  artery  gen- 
erally exceeds  that  of  the  parent  trunk;  and  as  the  distance  from  the 
origin  is  increased,  the  area  of  the  combined  branches  is  increased  also. 

After  death,  arteries  are  usually  found  dilated  (not  collapsed  as  the 
veins  are)  and  empty,  and  it  was  to  this  fact  that  their  name  was  given 
them,  as  the  ancients  believed  that  they  conveyed  air  to  the  various  parts 
of  the  body.  As  regards  the  arterial  system  of  the  lungs  (pulmonary 
system)  it  begins  at  the  right  ventricle  in  the  pulmonary  artery,  and  is 
distributed  much  as  the  arteries  belonging  to  the  general  systemic  cir- 
culation. 

Structure. — The  walls  of  the  arteries  are  composed  of  three  principal 
coats,  termed  the  external  or  tunica  adventitia,  the  middle  or  tunica 
madia,  and  the  internal  coat  or  tunica  intima. 

The  external  coat  or  tunica  adventitia  (Figs.  107  and  111,  t.  a.),  the 
strongest  and  toughest  part  of  the  wall  of  the  artery,  is  formed  of  areolar 


FIG.  107. 


Fio.  108. 


FIG.  107.— Minute  artery  viewed  in  longitudinal  section,  e.  Nucleated  endothelial  membrane, 
With  faint  nuclei  in  lumen,  looked  at  from  above,  i.  Thin  elastic  tunica  intima.  m.  Muscular  coat 
or  tunica  media.  «,  Tunica  adventitia.  (Klein  and  Noble  Smith.)  X  250. 

FIG.  108.— Portion  of  fenestrated  membrane  from  the  femoral  artery.  X  200.  a,  6,  c.  Perfo- 
rations. t.Henle.) 

tissue,  with  which  is  mingled  throughout  a  network  of  elastic  fibres. 
At  the  inner  part  of  this  outer  coat  the  elastic  network  forms  in  most 
arteries  so  distinct  a  layer  as  to  be  sometimes  called  the  external  elastic 
coat  (Fig.  123,  e.e.). 

The  middle  coat  (Fig.  107,  m)  is  composed   of  both  muscular  and 
VOL.  I.— 9 


130 


HAND-BOOK    OF    PHYSIOLOGY. 


elastic  fibres,  with  a  certain  proportion  of  areolar  tissue.  In  the  larger 
arteries  (Fig.  110)  its  thickness  is  comparatively  as  well  as  absolutely 
much  greater  than  in  the  small,  constituting,  as  it  does,  the  greater  part 
of  the  arterial  wall. 

The  muscular  fibres,  which  are  of  the  unstriped  variety  (Fig.  109)  are 
-arranged  for  the  most  part  transversely  to  the  long  axis  of  the  artery 
•(Fig.  107,  m);  while  the  elastic  element,  taking  also  a  transverse  direc- 
tion, is  disposed  in  the  form  of  closely  interwoven  and  branching  fibres, 
which  intersect  in  all  parts  the  layers  of  muscular  fibre.  In  arteries  of 


FIG.  109. 


FIG.  110. 


FIG.  109.— Muscular  fibre-cells  from  human  arteries,  magnified  350  diameters.  (Kolliker.)  a. 
Nucleus,  b.  A  fibre-cell  treated  with  acetic  acid. 

FIG.  110.— Transverse  section  of  aorta  through  internal  and  about  half  the  middle  coat.  a.  Lin- 
ing eudothelium  with  the  nuclei  of  the  cells  only  shown.  6.  Subepithelial  layer  of  connective  tissue. 
c,  d.  Elastic  tunica  intima  proper,  with  fibrils  running  circularly  or  longitudinally.  e,f.  Middle  coat. 
consisting  of  elastic  fibres  arranged  longitudinally,  with  muscle-fibres  cut  obliquely,  or  longitudinally. 
(Klein.) 

various  size  there  is  a  difference  in  the  proportion  of  the  muscular  and 
elastic  element,  elastic  tissue  preponderating  in  the  largest  arteries,  while 
this  condition  is  reversed  in  those  of  medium  and  small  size. 

The  internal  coat  is  formed  by  layers  of  elastic  tissue,  consisting  in 
part  of  coarse  longitudinal  branching  fibres,  and  in  part  of  a  very  thin 
and  brittle  membrane  which  possesses  little  elasticity,  and  is  thrown  into 
folds  or  wrinkles  when  the  artery  contracts.  This  latter  membrane, 
the  striated  or  fenestrated  coat  of  Henle  (Fig.  108),  is  peculiar  in  its  ten- 
dency to  curl  up,  when  peeled  off  from  the  artery,  and  in  the  perforated 


CIRCULATION    OF    THE    BLOOD. 


131 


mid  streaked  appearance  which  it  presents  under  the  microscope.  Its 
inner  surface  is  lined  with  a  delicate  layer  of  endotfcelium,  composed  of 
elongated  cells  (Fig.  112,  a),  which  make  it  smooth  and  polished,  and 
furnish  a  nearly  impermeable  surface,  along  which  the  blood  may  flow 
with  the  smallest  possible  amount  of  resistance  from  friction. 

Immediately  external  to  the  endothelial  lining  of  the  artery  is  fine 
connective  tissue,  sub-endothelial  layer,  with  branched  corpuscles.  Thus 
the  internal  coat  consists  of  three  parts,  (a)  an  endothelial  lining,  (b)  the 
sub-endothelial  layer,  and  (c)  elastic  layers. 

Vasa  Vasorum. — The  walls  of  the  arteries,  with  the  possible  excep- 
tion of  the  endothelial  lining  and  the  layers  of  the  internal  coat  immedi- 
ately outside  it,  are  not  nourished  by  the  blood  which  they  convey,  but 
are,  like  other  parts  of  the  body,  supplied  with  little  arteries,  ending  in 


FIG.  111. 

FIG.  111.— Transverse  section  of  small  artery  from  soft  palate,    e,  endothelial  lining,  the  nuclei 
of  the  cells  are  shown;  i,  elastic  tissue  of  the  intima,  which  is  a  good  deal  folded;  c.  m.  circular  mus- 


.  showing  the 

Artery.  The  endothelial  cells  are  long  and  narrow ;  the  trans- 
vtM-st!  markings  indicate  the  muscular  cout.  t.  a.  Tunica  adventitia.  v.  Vein,  showing  the  shorter 
.and  wider  endothelial  cells  with  which  it  is  lined,  c,  c.  Two  capillaries  entering  the  vein.  (Schofield.) 

capillaries  and  veins,  which,  branching  throughout  the  external  coat, 
extend  for  some  distance  into  the  middle,  but  do  not  reach  the  internal 
coat.  These  nutrient  vessels  are  called  vasa  vasorum. 

Lymphatics  of  Arteries  and  Veins.— Lymphatic  spaces  are  pres- 
ent in  the  coats  of  both  arteries  and  veins;  but  in  the  tunica  adventitia 
or  external  coat  of  large  vessels  they  form  a  distinct  plexus  of  more  or  less 
tubular  vessels.  In  smaller  vessels  they  appear  as  sinous  spaces  lined  by 
endothelium.  Sometimes,  as  in  the  arteries  of  the  omentum,  mesentery, 
and  membranes  of  the  brain,  in  the  pulmonary,  hepatic,  and  splenic 
arteries,  the  spaces  are  continuous  with  vessels  which  distinctly  ensheath 


132 


HAND-BOOK    OF    PHYSIOLOGY. 


ihem—perivascular  lymphatic  sheaths  (Fig.  121).     Lymph  channels  are 
said  to  be  present  siso  in  the  tunica  media. 

Nervi  Vasorum. — Most  of  the  arteries  are  surrounded  by  a  plexus 
of  sympathetic  nerves,  which  twine  around  the  vessel  very  much  like  ivy 
round  a  tree:  and  ganglia  are  found  at  frequent  intervals.  The  smallest 


f  '  Iff 


FIG.  113.— Blood-vessels  from  mesocolon  of  rabbit,  a.  Artery,  with  two  branches,  showing  tr.  n. 
nuclei  of  transverse  muscular  fibres ;  I.  n.  nuclei  of  endothelial  lining;  t.  a.  tunica  advent! tia.  v. 
Vein.  Here  the  transverse  nuclei  are  more  oval  than  those  of  the  artery.  The  vein  receives  a  small 
branch  at  the  lower  end  of  the  drawing:  it  is  distinguished  from  the  artery  among  other  things  by  its 
straighter  course  and  larger  calibre,  c.  Capillary,  showing  nuclei  of  endothelial  cells.  X  300. 
(Schofield.) 


arteries  and  capillaries  are  also  surrounded  by  a  very  delicate  network  of 
similar  nerve-fibres,  many  of  which  appear  to  end  in  the  nuclei  of  the 
transverse  muscular  fibres  (Fig.  122).  It  is  through  these  plexuses  that 
the  calibre  of  the  vessels  is  regulated  by  the  nervous  system  (p.  152). 

THE  CAPILLARIES. 

Distribution. — In  all  vascular  textures,  except  some  parts  of  the 
corpora  cavernosa  of  the  penis,  and  of  the  uterine  placenta,  and  of  the 
spleen,  the  transmission  of  the  blood  from  the  minute  branches  of  the 
arteries  to  the  minute  veins  is  effected  through  a  network  of  microscopic 
vessels,  called  capillaries.  These  may  be  seen  in  all  minutely  injected 
preparations;  and  during  life,  in  any  transparent  vascular  parts, — such 
as  the  web  of  the  frog's  foot,  the  tail  or  external  branchiae  of  the  tadpole, 
or  the  wing  of  the  bat. 

The  branches  of  the  minute  arteries  form  repeated  anastomoses  with 


(  IliCTLATION    OF    THE    BLOOD. 


133 


other,  and  give  off  the  capillaries  which,  by  their  anastomoses,  com- 
pose a  continuous  and  uniform  network,  from  which  the  venous  radicles 
take  their  rise  (Fig.  114).  The  point  at  which  the 
arteries  terminate  and  the  minute  veins  commence, 
cannot  be  exactly  defined,  for  the  transition  is 
gradual;  but  the  capillary  network  has,  neverthe- 
less, this  peculiarity,  that  the  small  vessels  which 
compose  it  maintain  the  same  diameter  throughout: 
they  do  not  diminish  in  diameter  in  one  direction, 
like  arteries  and  veins;  and  the  meshes  of  the  net- 
work that  they  compose  are  more  uniform  in  shape 
and  size  than  those  formed  by  the  anastomoses  of 
the  minute  arteries  and  veins. 

Structure. — This  is  much  more  simple  than 
that  of  the  arteries  or  veins.  Their  walls  are  com- 
posed of  a  single  layer  of  elongated  or  radiate,  flat- 
tened and  nucleated  cells,  so  joined  and  dovetailed 
together  as  to  form  a  continuous  transparent  mem- 
brane (Fig.  115).  Outside  these  cells,  in  the  larger 
capillaries,  there  is  a  structureless,  or  very  finely 
fibrillated  membrane,  on  the  inner  surface  of  which 
they  are  laid  down. 

In  some  cases  this  external   membrane  is  nu- 
cleated, and  may  then  be  regarded  as  a  miniature  representative  of  the 
tunica  adventitia  of  arteries. 

Here  and  there,  at  the  junction  of  two  or  more  of  the  delicate  endo- 
thelial  cells  which  compose  the  capillary  wall,  pseudo-stomafa  may  be  seen 


FIG.  114.— Blood-vessels  of 
an  intestinal  villus,  repre- 
senting the  arrangement  of 
capillaries  between  the  ulti- 
mate venous  and  arterial 
branches ;  a,  a,  the  arteries ; 
6,  the  vein. 


FIG.  115.— Capillary  blood-vessels  from  the  omentum  of  rabbit,  showing  the  nucleated  endothe- 
Lal  membrane  of  which  they  are  composed.    (Klein  and  Noble  Smith.) 

resembling  those  in  serous  membranes  (p.  296).  The  endothelial  cells  are 
often  continuous  at  various  points  with  processes  of  adjacent  connective- 
tissue  corpuscles. 


134 


1LAKD-BOOK    OF    PHYSIOLOGY. 


Capillaries  are  surrounded  by  a  delicate  nerve-plexus  resembling,  in 
miniature,  that  of  the  larger  blood-vessels. 

The  diameter  of  the  capillary  vessels  varies  somewhat  in  the  different 
textures  of  the  body,  the  most  common  size  being  about  -s-oVoth  °f  an 
inch.  Among  the  smallest  may  be  mentioned  those  of  the  brain,  and 
of  the  follicles  of  the  mucous  membrane  of  the  intestines ;  among  the 
largest,  those  of  the  skin,  and  especially  those  of  the  medulla  of  bones. 

The  size  of  capillaries  varies  necessarily  in  different  animals  in  relation 
to  the  size  of  their  blood  corpuscles:  thus,  in  the  Proteus,  the  capillary 
circulation  can  just  be  discerned  with  the  naked  eye. 

The/orm  of  the  capillary  network  presents  considerable  variety  in  the 
different  textures  of  the  body:  the  varieties  consisting  principally  of  modi- 
fications of  two  chief  kinds  of  mesh,  the  rounded  and  the  elongated.  That 


FIG.  116. 


FIG.  117. 


FIG.  116.— Network  of  capillary  vessels  of  the  air-cells  of  the  horse's  lung  magnified,    a,  a,  cap- 
illaries proceeding  from  &,  ft,  terminal  branches  of  the  pulmonary  artery.    (Frey.) 

FIG.  117.— Injected  capillary  vessels  of  muscle  seen  with  a  low  magnifying  power.    (Sharpey.) 


kind  of  which  the  meshes  or  interspaces  have  a  roundish  form  is  the  most 
common,  and  prevails  in  those  parts  in  which  the  capillary  network  is 
most  dense,  such  as  the  lungs  (Fig.  116),  most  glands,  and  mucous  mem- 
branes, and  the  cutis.  The  meshes  of  this  kind  of  network  are  not  quite 
circular  but  more  or  less  angular,  sometimes  presenting  a  nearly  regular 
quadrangular  or  polygonal  form,  but  being  more  frequently  irregular. 
The  capillary  network  with  elongated  meshes  (Fig.  117)  is  observed  in 
parts  in  which  the  vessels  are  arranged  among  bundles  of  fine  tubes  or 
fibres,  as  in  muscles  and  nerves.  In  such  parts,  the  meshes  usually  have 
the  form  of  a  parallelogram,  the  short  sides  of  which  may  be  from  three 
to  eight  or  ten  times  less  than  the  long  ones;  the  long  sides  always  corre- 
sponding to  the  axis  of  the  fibre  or  tube,  by  which  it  is  placed.  The  ap- 
pearance of  both  the  rounded  and  elongated  meshes  is  much  varied 


CIRCULATION    OF    THE    BLOOD.  135 

according  as  the  vessels  composing  them  have  a  straight  or  tortuous  form. 
Sometimes  the  capillaries  have  a  looped  arrangement,  a  single  capillary 
projecting  from  the  common  network  into  some  prominent  organ,  and 
returning  after  forming  one  or  more  loops,  as  in  the  papillae  of  the  tongue 
and  skin. 

The  number  of  the  capillaries  and  the  size  of  the  meshes  in  different 
parts  determine  in  general  the  degree  of  vascularity  of  those  parts.  The 
parts  in  which  the  network  of  capillaries  is  closest,  that  is,  in  which  the 
meshes  or  interspaces  are  the  smallest,  are  the  lungs  and  the  choroid 
membrane  of  the  eye.  In  the  iris  and  ciliary  body,  the  interspaces  are 
somewhat  wider,  yet  very  small.  In  the  human  liver  the  interspaces  are 
of  the  same  size  or  even  smaller  than  the  capillary  vessels  themselves. 
In  the  human  lung  they  are  smaller  than  the  vessels;  in  the  human 
kidney,  and  in  the  kidney  of  the  dog,  the  diameter  of  the  injected  capil- 
laries, compared  with  that  of  the  interspaces,  is  in  the  proportion  of  one 
to  four,  or  of  one  to  three.  The  brain  receives  a  very  large  quantity  of 
blood;  but  the  capillaries  in  which  the  blood  is  distributed  through  its 
substance  are  very  minute,  and  less  numerous  than  in  some  otherj^arts. 
Their  diameter,  according  to  E.  H.  Weber,  compared  with  the  long  diam- 
eter of  the  meshes,  being  in  the  proportion  of  one  to  eight  or  ten ;  com- 
pared with  the  transverse  diameter,  in  the  proportion  of  one  to  four  or 
six.  In  the  mucous  membranes — for  example  in  the  conjunctiva  and  in 
the  cutis  vera,  the  capillary  vessels  are  much  larger  than  in  the  brain, 
and  the  interspaces  narrower, — namely,  not  more  than  three  or  four  times 
wider  than  the  vessels.  In  the  periosteum  the  meshes  are  much  larger. 
In  the  external  coat  of  arteries,  the  width  of  the  meshes  is  ten  times  that 
of  the  vessels  (Henle). 

It  may  be  held  as  a  general  rule,  that  the  more  active  the  functions  of 
an  organ  are,  the  more  vascular  it  is.  Hence  the  narrowness  of  the  inter- 
spaces in  all  glandular  organs,  in  mucous  membranes,  and  in  growing 
parts;  their  much  greater  width  in  bones,  ligaments,  and  other  very 
tough  and  comparatively  inactive  tissues;  and  the  usually  complete 
absence  of  vessels  in  cartilage,  and  such  parts  as  those  in  which,  prob- 
ably, very  little  vital  change  occurs  after  they  are  once  formed. 

THE  VEINS. 

Distribution. — The  venous  system  begins  in  small  vessels  which  are 
slightly  larger  than  the  capillaries  from  which  they  spring.  These  vessels 
are  gathered  up  into  larger  and  larger  trunks  until  they  terminate  (as 
regards  the  systemic  circulation)  in  the  two  venae  cavae  and  the  coronary 
veins,  which  enter  the  right  auricle,  and  (as  regards  the  pulmonary  circu- 
lation) in  four  pulmonary  veins,  which  enter  the  left  auricle.  The  capac- 
ity of  the  veins  diminishes  as  they  approach  the  heart;  but,  as  a  rule, 


136  HAND-BOOK    OF    PHYSIOLOGY. 

the  capacity  of  the  veins  exceeds  by  several  times  (twice  or  three  times) 
that  of  their  corresponding  arteries.  The  pulmonary  veins,  however, 
are  an  exception  to  this  rule,  as  they  do  not  exceed  in  capacity  the 
pulmonary  arteries.  The  veins  are  found  after  death  as  a  rule  to  be  more 
or  less  collapsed,  and  often  to  contain  blood.  The  veins  are  usually  dis- 
tributed in  a  superficial  and  a  deep  set  which  communicate  frequently  in 
their  course. 

Structure. — In  structure  the  coats  of  veins  bear  a  general  resem- 
blance to  those  of  arteries  (Fig.   118).      Thus,   they  possess  an  outer, 


TIG.  118.— Transverse  section  through  a  small  artery  and  vein  of  the  mucous  membrane  of  a 
Child's  epiglottis:  the  contrast  between  the  thick- walled  artery  and  the  thin- walled  vein  is  well  shown. 
A.  Artery,  the  letter  is  placed  in  the  lumen  of  the  vessel,  e.  Endothelial  cells  with  nuclei  clearly  vis- 
ible: these  cells  appear  very  thick  from  the  contracted  state  of  the  vessel.  Outside  it  a  double  wavy 
line  marks  the  elastic  tunica  intima.  ra.  Tunica  media  forming  the  chief  part  of  arterial  wall  and 
consisting  of  unstriped  muscular  fibres  circularly  arranged:  their  nuclei  are  well  seen,  a.  Part  of 
the  tunica  adventitia  showing  bundles  of  connective-tissue  fibres  in  section,  with  the  circular  nuclei 
of  the  connective-tissue  corpuscles.  This  coat  gradually  merges  into  the  surrounding  connective- 
tissue.  V.  In  the  lumen  of  the  vein.  The  other  letters  indicate  the  same  as  in  the  artery.  The  mus- 
cular coat  of  the  vein  (m)  is  seen  to  be  much  thinner  than  that  of  the  artery.  X  350.  (Klein  and 
Noble  Smith.) 

middle,  and  internal  coat.  The  outer  coat  is  constructed  of  areolar  tissue 
like  that  of  the  arteries,  but  is  thicker.  In  some  veins  it  contains  mus- 
cular fibre-cells,  which  are  arranged  longitudinally. 

The  middle  coat  is  considerably  thinner  than  that  of  the  arteries;  and, 
although  it  contains  circular  unstriped  muscular  fibres  or  fibre-cells,  these 
are  mingled  with  a  larger  proportion  of  yellow  elastic  and  white  fibrous 
tissue.  In  the  large  veins,  near  the  heart,  namely  the  vencs  caves  and 
pulmonary  veins,  the  middle  coal;  is  replaced,  for  some  distance  from  the 
heart,  by  circularly  arranged  striped  muscular  fibres,  continuous  with 
those  of  the  auricles. 


CIRCULATION    OF    THE    BLOOD. 


137 


The  internal  coat  of  veins  is  less  brittle  than  the  corresponding  coat 
of  an  artery,  but  in  other  respects  resembles  it  closely. 

Valves.— The  chief  influence  which  the  veins  have  in  the  circulation, 
is  effected  with  the  help  of  the  valves,  which  are  placed  in  all  veins  sub- 
ject to  local  pressure  from  the  muscles  between  or  near  which  they  run. 
The  general  construction  of  these  valves  is  similar  to  that  of  the  semi- 
lunar  valves  of  the  aorta  and  pulmonary  artery,  already  described;  but 
their  free  margins  are  turned  in  the  opposite  direction,  i.e.,  toward  the 
heart,  so  as  to  stop  any  movement  of  blood  backward  in  the  veins.  They 
are  commonly  placed  in  pairs,  at  various  distances  in  different  veins,  but 
almost  uniformly  in  each  (Fig.  119).  In  the  smaller  veins,  single  valves 
are  often  met  with;  and  three  or  four  are  sometimes  placed  together,  or 
near  one  another,  in  the  largest  veins,  such  as  the  subclavian,  and  at 
their  junction  with  the  jugular  veins.  The  valves  are  semilunar;  the 


FIG.  119. — Diagram  showing  valves  of  veins.  A,  part  of  a  vein  laid  open  and  spread  out.  with  two 
pairs  of  valves.  B.  Longitudinal  section  of  a  vein,  snowing  the  apposition  of  the  edges  of  the  valves 
in  their  closed  state,  c,  portion  of  a  distended  vein,  exhibiting  a  swelling  in  the  situation  of  a  pair 
of  valves. 

unattached  edge  being  in  some  examples  concave,  in  others  straight. 
They  are  composed  of  inextensile  fibrous  tissue,  and  are  covered  with 
endothelium  like  that  lining  the  veins.  During  the  period  of  their  in- 
action, when  the  venous  blood  is  flowing  in  its  proper  direction,  they 
lie  by  the  sides  of  the  veins;  but  when  in  action,  they  close  together  like 
the  valves  of  the  arteries,  and  offer  a  complete  barrier  to  any  backward 
movement  of  the  blood  (Figs.  119  and  120).  Their  situation  in  the 
superficial  veins  of  the  forearm  is  readily  discovered  by  pressing  along  its 
surface,  in  a  direction  opposite  to  the  venous  current,  i.e.,  from  the 
elbow  toward  the  wrist;  when  little  swellings  (Fig.  119,  c)  appear  in  the 
position  of  each  pair  of  valves.  These  swellings  at  once  disappear  when 
the  pressure  is  relaxed. 

Valves  are  not  equally  numerous  in  all  veins,  and  in  many  they  are 
absent  altogether.  They  are  most  numerous  in  the  veins  of  the  extremi- 
ties, and  more  so  in  those  of  the  leg  than  the  arm.  They  are  commonly 
absent  in  veins  of  less  than  a  line  in  diameter,  and,  as  a  general  rule, 


138  HAND-BOOK    OF    PHYSIOLOGY. 

there  are  few  or  none  in  those  which  are  not  subject  to  muscular  pressure. 
Among  those  veins  which  have  no  valves  may  be  mentioned  the  superior 
and  inferior  vena  cava,  the  trunk  and  branches  of  the  portal  vein,  'the 


FIG.  120.— A,  vein  with  valves  open.    B,  vein  with  valves  closed:  stream  of  blood  passing  off  by 
lateral  channel.    (Dalton.) 

hepatic  and  renal  veins,  and  the  pulmonary  veins;  those  in  the  interior 
of  the  cranium  and  vertebral  column,  those  of  the  bones,  and  the  trunk 
and  branches  of  the  umbilical  vein  are  also  destitute  of  valves. 


CIRCULATION  IN  THE  ARTERIES. 

Functions  of  the  External  Coat  of  Arteries. — The  external  coat 
forms  a  strong  and  tough  investment,  which,  though  capable  of  exten- 
sion, appears  principally  designed  to  strengthen  the  arteries  and  to  guard 
against  their  excessive  distension  by  the  force  of  the  heart's  action.  It  is 
this  coat  which  alone  prevents  the  complete  severance  of  an  artery  when 
a  ligature  is  tightly  applied;  the  internal  and  middle  coats  being  divided. 
In  it,  too,  the  little  vasa  vasorum  (p.  131)  find  a  suitable  tissue  in  which 
to  subdivide  for  the  supply  of  the  arterial  coats. 

Functions  of  the  Elastic  Tissue  in  Arteries.— The  purpose  of 
the  elastic  tissue,  which  enters  so  largely  into  the  formation  of  all  the 
coats  of  the  arteries,  is,  (a)  to  guard  the  arteries  from  the  suddenly 
exerted  pressure  to  which  they  are  subjected  at  each  contraction  of  the 
ventricles.  In  every  such  contraction,  the  contents  of  the  ventricles  are 
forced  into  the  arteries  more  quickly  than  they  can  be  discharged  into 
and  through  the  capillaries.  The  blood  therefore,  being,  for  an  instant, 
resisted  in  its  onward  course,  a  part  of  the  force  with  which  it  was  im- 


CIRCULATION    OF    THE    BLOOD. 


139 


pelled  is  directed  against  the  sides  of  the  arteries;  under  this  force  their 
elastic  walls  dilate,  stretching  enough  to  receive  the  blood,  and  as  they 
stretch,  becoming  more  tense  and  more  resisting.  Thus,  by  yielding, 
they  break  the  shock  of  the  force  impelling 
the  blood.  On  the  subsidence  of  the  pressure, 
when  the  ventricles  cease  contracting,  the  arte- 
ries aiv  able,  by  the  same  elasticity,  to  resume 
their  former  calibre;  (b)  It  equalizes  the  cur- 
rent of  the  blood  by  maintaining  pressure  on 
it  in  the  arteries  during  the  periods  at  which 
the  ventricles  are  at  rest  or  dilating.  If  the 
arteries  had  -been  rigid  tubes,  the  blood,  in- 
stead of  flowing,  as  it  does,,  in  a  constant 
stream,  would  have  been  propelled  through 
the  arterial  system  in  a  series  of  jerks  corre- 
sponding to  the  ventricular  contractions,  writh 
intervals  of  almost  complete  rest  during  the 
inaction  of  the  ventricles.  But  in  the  actual 
condition  of  the  arteries,  the  force  of  the  suc- 
cessive contractions  of  the  ventricles  is  ex- 
pended partly  in  the  direct  propulsion  of  the 
blood,  and  partly  in  the  dilatation  of  the  elastic 
arteries;  and  in  the  intervals  between  the  con- 
tractions of  the  ventricles,  the  force  of  the  re- 
coil is  employed  in  continuing  the  same  direct 
propulsion.  Of  course,  the  pressure  they  ex- 
ercise is  equally  diffused  in  every  direction, 
and  the  blood  tends  to  move  backward  as  well 
as  onward,  but  all  movement  backward  is  pre- 
vented by  the  closure  of  the  semilunar  arterial  valves  (p.  114),  which 
takes  place  at  the  very  commencement  of  the  recoil  of  the  arterial  walls. 
By  this  exercise  of  the  elasticity  of  the  arteries,  all  the  force  of  the 
ventricles  is  made  advantageous  to  the  circulation;  for  that  part  of  their 
force  which  is  expended  in  dilating  the  arteries,  is  restored  in  full  when 
they  recoil.  There  is  thus  no  loss  of  force;  but  neither  is  there  any  gain, 
for  the  elastic  walls  of  the  artery  cannot  originate  any  force  for  the  propul- 
sion of  the  blood — they  only  restore  that  which  they  received  from  the 
ventricles.  The  force  with  which  the  arteries  are  dilated  every  time  the 
ventricles  contract,  might  be  said  to  be  received  by  them  in  store,  to  be  all 
given  out  again  in  the  next  succeeding  period  of  dilatation  of  the  ventricles. 
It  is  by  this  equalizing  influence  of  the  successive  branches  of  every  artery 
that,  at  length,  the  intermittent  accelerations  produced  in  the  arterial 
current  by  the  action  of  the  heart,  cease  to  be  observable,  and  the  jetting 
stream  is  converted  into  the  continuous  and  equable  movement  of  the 


Fi».  121.— Surface  view  of  an 
artery  from  the  mesentery  of  a 
frog,  ensheathed  in  a  perivascular 
lymphatic  vessel,  a.  The  artery, 
with  its  circular  muscular  coat 
(media)  indicated  by  broad  trans- 
verse markings,  with  an  indication 
of  the  adventitia  outside.  I.  Lym- 
phatic vessel ;  its  wall  is  a  simple 
endothelial  membrane.  (Klein  and 
Noble  Smith.) 


140 


HAND-BOOK    OF    PHYSIOLOGY. 


blood  which  we  see  in  the  capillaries  and  veins.  In  the  production  of  a 
continuous  stream  of  blood  in  the  smaller  arteries  and  capillaries,  the 
resistance  which  is  offered  to  the  blood-stream  in  these  vessels  (p.  158), 
is  a  necessary  agent.  Were  there  no  greater  obstacle  to  the  escape  of 
blood  from  the  larger  arteries  than  exists  to  its  entrance  into  them  from 
the  heart,  the  stream  would  be  intermittent,  notwithstanding  the  elas- 
ticity of  the  walls  of  the  arteries. 

(c.)  By  means  of  the  elastic  tissue  in  their  walls  (and  of  the  muscular 
tissue  also),  the  arteries  are  enabled  to  dilate  and  contract  readily  in  cor- 
respondence with  any  temporary  increase  or  diminution  of  the  total 
quantity  of  blood  in  the  body;  and  within  a  certain  range  of  diminution 


FIG.  122. 


FIG.  123. 


FIG.  122.— Ramification  of  nerves  and  termination  in  the  muscular  coat  of  a  small  artery  of  the 
frog.  (Arnold.) 

FIG.  123.— Transverse  section  through  a  large  branch  of  the  inferior  mesenteric  artery  of  a  pig. 
e,  enclothelial  membrane;  i,  tunica  elastica  interna,  no  subendothelial  layer  is  seen;  m,  muscular  tu- 
nica media,  containing  only  a  few  wavy  elastic  fibres;  ee,  tunica  elastica  externa,  dividing  the  media 
from  the  connective  tissue  adventitia,  a.  (Klein  and  Noble  Smith.)  x  350. 

of  the  quantity,  still  to  exercise  due  pressure  on  their  contents;  (d.)  The 
elastic  tissue  assists  in  restoring  the  normal  state  after  diminution  of  its 
calibre,  whether  this  has  been  caused  by  a  contraction  of  the  muscular 
coat,  or  the  temporary  application  of  a  compressing  force  from  without. 
This  action  is  well  shown  in  arteries  <which,  having  contracted  by  means 
of  their  muscular  element,  after  death,  regain  their  average  patency  on 
the  cessation  of  post-mortem  rigidity  (p.  142).  (e.}  By  means  of  their 
elastic  coat  the  arteries  are  enabled  to  adapt  themselves  to  the  different 
movements  of  the  several  parts  of  the  body. 

Tension  of  Arteries, — The  natural  state  of  all  arteries,  in  regard  at  least 
to  their  length,  is  one  of  tension — they  are  always  more  or  less  stretched, 
and  ever  ready  to  recoil  by  virtue  of  their  elasticity,  whenever  the  oppos- 


CIRCULATION    OF    THE    BLOOD.  141 

ing  force  is  removed.     The  extent  to  which  the  divided  extremities  of 
arteries  retract  is  a  measure  of  this  tension,  not  of  their  elasticity.   (Savory. ) 

Functions  of  the  Muscular  Coat— The  most  important  office  of 
the  muscular  coat  is,  (1)  that  of  regulating  the  quantity  of  blood  to  be 
received  by  each  part  or  organ,  and  of  adjusting  it  to  the  requirements 
of  each,  according  to  various  circumstances,  but,  chiefly,  according  to  the 
activity  with  which  the  functions  of  each  are  at  different  times  performed. 
The  amount  of  work  done  by  each  organ  of  the  body  varies  at  different 
times,  and  the  variations  often  quickly  succeed  each  other,  so  that,  as  in 
the  brain,  for  example,  during  sleep  and  waking,  within  the  same  hour 
a  part  may  be  now  very  active  and  then  inactive.  In  all  its  active  exer- 
cise of  function,  such  a  part  requires  a  larger  supply  of  blood  than  is  suffi- 
cient for  it  during  the  times  when  it  is  comparatively  inactive.  It  is  evi 
dent  that  the  heart  cannot  regulate  the  supply  to  each  part  at  different 
periods;  neither  could  this  be  regulated  by  any  general  and  uniform  con- 
traction of  the  arteries;  but  it  may  be  regulated  by  the  power  which  the 
arteries  of  each  part  have,  in^  their  muscular  tissue,  of  contracting  so  as 
to  diminish,  and  of  passively  dilating  or  yielding  so  as  to  permit  an  in- 
crease of  the  supply  of  blood,  according  to  the  requirements  of  the  part  to 
which  they  are  distributed.  And  thus,  while  the  ventricles  of  the  heart 
determine  the  total  quantity  of  blood,  to  be  sent  onward  at  each  contrac- 
tion, and  the  force  of  its  propulsion,  and  while  the  large  and  merely  elastic 
arteries  distribute  it  and  equalize  its  stream,  the  smaller  arteries,  in  addi- 
tion, regulate  and  determine,  by  means  of  their  muscular  tissue,  the  propor- 
tion of  the  whole  quantity  of  blood  which  shall  be  distributed  to  each  part. 

It  must  be  remembered,  however,  that  this  regulating  function  of  the 
arteries  is  itself  governed  and  directed  by  the  nervous  system  (vaso-motor 
centres  and  fibres). 

Another  function  of  the  muscular  element  of  the  middle  coat  of  arteries 
is  (2),  to  co-operate  with  the  elastic  in  adapting  the  calibre  of  the  ves- 
sels to  the  quantity  of  blood  which  they  contain.  For  the  amount  of 
fluid  in  the  blood-vessels  varies  very  considerably  even  from  hour  to  hour, 
and  can  never  be  quite  constant;  and  were  the  elastic  tissue  only  present, 
the  pressure  exercis'ed  by  the  walls  of  the  containing  vessels  on  the  con- 
tained blood  would  be  sometimes  very  small,  and  sometimes  inordinately 
great.  The  presence  of  a  muscular  element,  however,  provides  for  a 
certain  uniformity  in  the  amount  of  pressure  exercised;  and  it  is  by  this 
adaptive,  uniform,  gentle,  muscular  contraction,  that  the  normal  tone  of  the 
blood-vessels  is  maintained.  Deficiency  of  this  tone  is  the  cause  of  the 
soft  and  yielding  pulse,  and  its  unnatural  excess,  of  the  hard  and  tense  one. 

The  elastic  and  muscular  contraction  of  an  artery  may  also  be  regarded 
as  fulfilling  a  natural  purpose  when  (3),  the  artery  being  cut,  it  first  limits 
and  then,  in  conjunction  with  the  coagulated  fibrin,  arrests  the  escape  of 
blood.  It  is  only  in  consequence  of  such  contraction  and  coagulation  that 


142  HAND-BOOK    OF    PHYSIOLOGY. 

we  are  free  from  danger  through  even  very  slight  wounds;  for  it  is  only 
when  the  artery  is  closed  that  the  processes  for  the  more  permanent  and 
secure  prevention  of  bleeding  are  established. 

(4)  There  appears  no  reason  for  supposing  that  the  muscular  coat 
assists,  to  more  than  a  very  small  degree,  in  propelling  the  onward  current 
of  blood. 

(1.)  When  a  small  artery  in  the  living  subject  is  exposed  to  the  air  or 
cold,  it  gradually  but  manifestly  contracts.  Hunter  observed  that  the 
posterior  tibial  artery  of  a  dog  when  laid  bare,  became  in  a  short  time  so 
much  contracted  as  almost  to  prevent  the  transmission  of  blood;  and  the 
observation  has  been  often  and  variously  confirmed.  Simple  elasticity 
could  not  effect  this. 

(2.)  When  an  artery  is  cut  across,  its  divided  ends  contract,  and  the 
orifices  may  be  completely  closed.  The  rapidity  and  completeness  of  this 
contraction  vary  in  different  animals;  they  are  generally  greater  in  young 
than  in  old  animals;  and  less,  apparently,  in  man  than  in  the  lower  ani- 
mals. This  contraction  is  due  in  part  to  elasticity,  but  in  part,  also,  to 
muscular  action;  for  it  is  generally  increased  by  the  application  of  cold, 
or  of  any  simple  stimulating  substances,  or  by  mechanically  irritating  the 
cut  ends  of  the  artery,  as  by  picking  or  twisting  them. 

(3.)  The  contractile  property  of  arteries  continues  many  hours  after 
death,  and  thus  affords  an  opportunity  of  distinguishing  it  from  their 
elasticity.  When  a  portion  of  an  artery  of  a  recently  killed  animal  is  ex- 
posed, it  gradually  contracts,  and  its  canal  may  be  thus  completely  closed: 
in  this  contracted  state  it  remains  for  a  time,  varying  from  a  few  hours 
to  two  days:  then  it  dilates  again,  and  permanently  retains  the  same  size. 

This  persistence  of  the  contractile  property  after  death  was  well  shown 
in  an  observation  of  Hunter,  which  may  be  mentioned  as  proving,  also, 
the  greater  degree  of  contractility  possessed  by  the  smaller  than  by  the 
larger  arteries.  Having  injected  the  uterus  of  a  cow,  which  had  been 
removed  from  the  animal  upward  of  twenty-four  hours,  he  found,  after 
the  lapse  of  another  day,  that  the  larger  vessels  had  become  much  more 
turgid  than  when  he  injected  them,  and  that  the  smaller  arteries  had 
contracted  so  as  to  force  the  injection  back  into  the  larger  ones. 

THE  PULSE. 

If  one  extremity  of  an  elastic  tube  be  fastened  to  a  syringe,  and  the 
other  be  so  constricted  as  to  present  an  obstacle  to  the  escape  of  fluid, 
we  shall  have  a  rough  model  of  what  is  present  in  the  living  body: — The 
syringe  representing  the  heart,  the  elastic  tube  the  arteries,  and  the  con- 
tracted orifice  the  arterioles  (smallest  arteries)  and  capillaries.  If  the 
apparatus  be  filled  with  water,  and  if  a  finger-tip  be  placed  on  any 
part  of  the  elastic  tube,  there  will  be  felt  with  every  action  of  the  syringe, 
an  impulse  or  beat,  which  corresponds  exactly  with  what  we  feel  in  the 
arteries  of  the  living  body  with  every  contraction  of  the  heart,  and  call 
the  pulse.  The  pulse  is  essentially  caused  by  an  expansion  wave,  which 
is  due  to  the  injection  of  blood  into  an  already  full  aorta;  which  blood 


CIRCULATION    OF    THE    BLOOD.  14 3 

expanding  the  vessel  produces  the -pulse  in  it,  almost  coincidently  with 
the  systole  of  the  left  ventricle.  As  the  force  of  the  left  ventricle,  however, 
is  not  expended  in  dilating  the  aorta  only,  the  wave  of  blood  passes  on, 
expanding  the  arteries  as  it  goes,  running  as  it  were  on  the  surface  of  the 
more  slowly  traveling  blood  already  contained  in  them,  and  producing  the 
pulse  as  it  proceeds. 

The  distension  of  each  artery  increases  both  its  length  and  its  diameter. 
In  their  elongation,  the  arteries  change  their  form,  the  straight  ones  be- 
coming slightly  curved,  and  those  already  curved  becoming  more  so,  but 
they  recover  their  previous  form  as  well  as  their  diameter  when  the  ven- 
tricular contraction  ceases,  and  their  elastic  walls  recoil.  The  increase  of 
their  curves  which  accompanies  the  distension  of  arteries,  and  the  succeed- 
ing recoil,  may  be  well  seen  in  the  prominent  temporal  artery  of  an  old 
person.  In  feeling  the  pulse,  the  finger  cannot  distinguish  the  sensation 
produced  by  the  dilatation  from  that  produced  by  the  elongation  and 


FIG.  124.— Diagram  of  the  mode  of  action  of  the  Sphygmograph. 

curving;  that  which  it  perceives  most  plainly,  however,  is  the  dilatation, 
or  return,  more  or  less,  to  the  cylindrical  form,  of  the  artery  which  has 
been  partially  flattened  by  the  finger. 

The  pulse — due  to  any  given  beat  of  the  heart — is  not  perceptible  at 
the  same  moment  in  all  the  arteries  of  the  body.  Thus, — it  can  be  felt 
in  the  carotid  a  very  short  time  before  it  is  perceptible  in  the  radial  artery, 
and  in  this  vessel  again  before  the  dorsal  artery  of  the  foot.  The  delay 
in  the  beat  is  in  proportion  to  the  distance  of  the  artery  from  the  heart, 
but  the  difference  in  time  between  the  beat  of  any  two  arteries  never 
exceeds  probably  -J  to  ^  of  a  second. 

A  distinction  must  be  carefully  made  between  the  passage  of  the  ivave 
along  the  arteries  and  the  velocity  of  the  stream  (p.  165)  of  blood.  Both 
wave  and  current  are  present;  but  the  rates  at  which  they  trawl  are  very 
different;  that  of  the  wave  16 -5  to  33  feet  per  second  (5  to  10  metres) 
being  twenty  or  thirty  times  as  great  as  that  of  the  current. 

The  Sphygmograph. — A  great  deal  of  light  has  been  thrown  on 
what  may  be  called  the  form  of  the  pulse  by  the  sphygmograph  (Figs. 
124  and  125).  The  principle  on  which  the  sphygmograph  acts  is  very 


144 


HAND-BOOK    OF    PHYSIOLOGY. 


simple  (see  Fig.  124).  The  small  button  replaces  the  finger  in  the  act  of 
taking  the  pulse,  and  is  made  to  rest  lightly  on  the  artery,  the  pulsations 
of  which  it  is  desired  to  investigate.  The  up-and-down  movement  of  the 
button  is  communicated  to  the  lever,  to  the  hinder  end  of  which  is  at- 
tached a  slight  spring,  which  allows  the  lever  to  move  up,  at  the  same 
time  that  it  is  just  strong  enough  to  resist  its  making  any  sudden  jerk, 


Fia.  125.— The  Sphygmograph  applied  to  the  arm. 

and  in  the  interval  of  the  beats  also  to  assist  in  bringing  it  back  to  its 
original  position.  For  ordinary  purposes  the  instrument  is  bound  on  the 
wrist  (Fig.  125). 

It  is  evident  that  the  beating  of  the  pulse  with  the  reaction  of  the 
spring  wrill  cause  an  up-and-down  movement  of  the  lever,  the  pen  of  which 
will  write  the  effect  on  a  smoked  card,  which  is  made  to  move  by  clock- 
work in  the  direction  of  the  arrow.  Thus  a  tracing  of  the  pulse  is  ob- 
tained, and  in  this  way  much  more  delicate  effects  can  be  seen,  than  can 
be  felt  on  the  application  of  the  finger. 

The  pulse-tracing  differs  somewhat  according  to  the  artery  upon  which 
the  sphygmograph  is  applied,  but  its  general  characters  are  much  the 
same  in  all  cases.  It  consists  of: — A  sudden  upstroke  (Fig.  126,  A),  which 

is  somewhat  higher  and  more  abrupt  in 
the  pulse  of  the  carotid  and  of  other 
arteries  near  the  heart  than  in  the  radial 
and  other  arteries  more  remote;  and  a 
gradual  decline  (B),  less  abrupt,  and 
therefore  taking  a  longer  time  than  (A). 
It  is  seldom,  however,  that  the  decline  is 
an  uninterrupted  fall:  it  is  usually  marked 
about  half-way  by  a  distinct  notch  (c), 
called  the  dicrotic  notch,  which  is  caused 
by  a  second  more  or  less  marked  ascent 
of  the  lever  at  that  point  by  a  second  wave 
called  the  dicrotic  wave  (D);  not  unfrequently  (in  which  case  the  tracing 
is  said  to  have  a  double  apex)  there  is  also  soon  after  the  commencement 
of  the  descent  a  slight  ascent  previous  to  the  dicrotic  notch,  this  is  called 
the  predicrotic  wave  (c),  and  in  addition  there  may  be  one  or  more 
slight  ascents  after  the  dicrotic,  called  post  dicrotic  (E). 


FIG.  126.— Diagram  of  pulse  tracing. 
A,  upstroke;  B,  down-stroke;  c,  predi- 
crotic wave ;  D,  dicrotic ;  E,  post  dicrotic 
wave. 


CIRCULATION    OF    THE    BLOOD.  145 

The  explanation  of  these  tracings  presents  some  difficulties,  not,  how- 
ever, as  regards  the  two  primary  factors,  viz.,  the  upstroke  and  down- 
stroke,  because  they  are  universally  taken  to  mean  the  sudden  injection 
of  blood  into  the  already  full  arteries,  and  that  this  passes  through  the 
artery  as  a  wave  and  expands  them,  the  gradual  fall  of  the  lever  signify- 
ing the  recovery  of  the  arteries  by  their  recoil.  It  may  be  demonstrated 
on  a  system  of  elastic  tubes,  such  as  was  described  above,  where  a  syringe 
pumps  in  water  at  regular  intervals,  just  as  well  as  on  the  radial  artery, 
or  on  a  more  complicated  system  of  tubes  in  which  the  heart,  the  arteries, 
the  capillaries  and  veins  are  represented,  which  is  known  as  an  arterial 
schema.  If  we  place  two  or  more  sphygmographs  upon  such  a  system 
of  tubes  at  increasing  distances  from  the  pump,  we  may  demonstrate 


FIG.  127.— Diagram  of  the  formation  of  the  pulse-tracing.    A,  percussion  wave;  B,  tidal  wave; 
C,  dicrotic  wave.    (Mahomed.) 

that  the  rise  of  the  lever  commences  first  in  that  nearest  the  pump, 
and  is  higher  and  more  sudden,  while  at  a  longer  distance  from  the  pump 
the  wave  is  less  marked,  and  a  little  later.  So  in  the  arteries  of  the  body 
the  wave  of  blood  gradually  gets  less  and  less  as  we  approach  the  periphery 
of  the  arterial  system,  and  is  lost  in  the  capillaries.  By  the  sudden  in- 
jection of  blood  two  distinct  waves  are  produced,  which  are  called  the 
tidal  and  percussion  waves.  The  tidal  wave  occurs  whenever  fluid  is 
injected  into  an  elastic  tube  (Fig.  127,  B),  and  is  due  to  the  expansion  of 
the  tube  and  its  more  gradual  collapse.  The  percussion  wave  occurs 
(Fig.  127,  A)  when  the  impulse  imparted  to  the  fluid  is  more  sudden; 
this  causes  an  abrupt  upstroke  of  the  lever,  which  then  falls  until  it  is. 
again  caught  up  perhaps  by  the  tidal  wave  which  begins  at  the  same  time 
but  is  not  so  quick. 
VOL.  I.— 10. 


146  HAND-BOOK    OF    PHYSIOLOGY. 

In  this  way,  generally  speaking,  the  apex  of  the  upstroke  is  double, 
the  second  upstroke,  the  so-called  predicrotic  elevation  of  the  lever, 
representing  the  tidal  wave.  The  double  apex  is  most  marked  in  tracings 
:from  large  arteries,  especially  when  their  tone  is  deficient.  In  tracings, 


FIG.  128.— Pulse-tracing  of  radial  artery,  somewhat  deficient  in  tone.    (Sanderson.) 

on  the  other  hand,  from  arteries  of  medium  size,  e.g.,  the  radial,  the 
upstroke  is  usually  single.  In  this  case  the  percussion-impulse  is  not 
sufficiently  strong  to  jerk  up  the  lever  and  produce  an  effect  distinct 
from  that  of  the  systolic  wave  which  immediately  follows  it,  and  which 


FIG.  129.— Pulse-tracing  of  radial  artery,  with  double  apex.    (Sanderson.) 

continues  and  completes  the  distension.  In  cases  of  feeble  arterial  ten- 
sion, however,  the  percussion-impulse  may  be  traced  by  the  sphygmo- 
graph,  not  only  in  the  carotid  pulse,  but  to  a  less  extent  in  the  radial  also 
(Fig.  129). 

The  interruptions  in  the  downstroke  are  called  the  katacrotic  waves, 
to  distinguish  them  from  an  interruption  in  the  upstroke,  called  the  an- 
acrotic wave,  which  is  occasionally  met  with  in  cases  in  which  the  predi- 
crotic or  tidal  wave  is  higher  than  the  percussion  wave. 


FIG.  130.— Anacrotic  pulse  from  a  case  of  aortic  aneurism.    A,  anacrotic  wave  (or  percussion 
wave).    B,  tidal  or  predicrotic  wave,  continued  rise  in  tension  (or  higher  tidal  wave). 

There  is  considerable  difference  of  opinion  as  to  whether  the  dicrotic 
wave  is  present  in  health  generally,  and  also  as  to  its  cause.  The  balance 
of  opinion  appears  to  be  in  favor  of  the  belief  of  its  presence  in  health, 
although  it  may  be  very  faint;  while,  at  any  rate,  in  certain  conditions 
not  necessarily  diseased,  it  becomes  so  marked  as  to  be  quite  plain  to  the 
unaided  finger.  Such  a  pulse  is  called  dicrotic.  Sometimes  the  dicrotic  rise 
exceeds  the  initial  upstroke,  and  the  pulse  is  then  called  liy per  dicrotic. 

As  to  the  cause  of  dicrotism,  one  opinion  is  that  it  is  due  to  a  recovery 


CIRCULATION    OF    THE    BLOOD. 


147 


of  pressure  during  the  elastic  recoil,  in  consequence  of  a  rebound  from 
the  periphery,  and  it  may  indeed  be  produced  on  a  schema  by  obstructing 
the  tube  at  a  little  distance  beyond  the  spot  where  the  sphygmograph 
is  placed.  Against  this  view,  however,  is  the  fact  that  the  notch 
appears  at  about  the  same  point  in  the 
downstroke  in  tracings  from  the  carotid 
and  from  the  radial,  and  not  first  in 
the  radial  tracing,  as  it  should  do,  since 
that  artery  is  nearer  the  periphery  than 
the  carotid,  and  as  it  does  in  the  cor- 
responding experiment  with  the  arterial 
schema  when  the  tube  is  obstructed. 
The  generally  accepted  notion  among 
clinical  observers,  is  that  the  dicrotic 
wave  is  due  to  the  rebound  from  the 
aortic  valves  causing  a  second  wave;  but 
the  question  cannot  be  considered  set- 
tled, and  the  presence  of  marked  dicro- 
tism  in  cases  of  haemorrhage,  of  anaemia, 
and  of  other  weakening  conditions,  as 
well  as  its  presence  in  cases  of  dimin- 
ished pressure  within  the  arteries,  would 
imply  that  it  might,  at  any  rate  some- 
times, be  due  to  the  altered  specific 
gravity  of  the  blood  within  the  vessels, 
either  directly  or  through  the  indirect 
effect  of  these  conditions  on  the  tone 
of  the  arterial  walls.  Waves  may  be 
produced  in  any  elastic  tube  when  a 
fluid  is  being  driven  through  it  with  an 
intermittent  force,  such  waves  being 
called  waves  of  oscillation  (M.  Foster). 
They  have  received  various  explana- 
tions. In  an  arterial  schema  they  vary 
with  the  specific  gravity  of  the  fluid 
used,  and  with  the  kind  of  tubing,  and  may  be  therefore  supposed  to 
vary  in  the  body  with  the  condition  of  the  blood  and  of  the  arteries. 

Some  consider  the  secondary  waves  in  the  downstroke  of  a  normal 
wave  to  be  due  to  oscillation;  but,  as  just  mentioned,  even  if  this  be  the 
case,  as  is  most  likely,  with  post-dicrotic  waves,  the  dicrotic  wave  itself  is 
almost  certainly  due  to  the  rebound  from  the  aortic  valves. 

The  anacrotic  notch  is  usually  associated  with  disease  of  the  arteries, 
e.g.,,  in  atheroma  and  aneurism.  The  dicrotic  notch  is  called  diastolic  or 
aortic,  and  indicates  closure  of  the  aortic  valves. 


Fio.  131.— Diagrams  of  pulse  curves  with 
exaggeration  of  one  or  other  of  the  three 
waves.  A,  percussion;  B,  tidal:  C,  dicrotic. 
1,  percussion  wave  very  marked;  2,  tidal 
wave  sudden;  3,  dicrotic  pulse  curve;  4  and 
5,  the  tidal  wave  very  exaggerated,  from 
high  tension.  (Mahomed.) 


148 


HAND-BOOK    OF    PHYSIOLOGY. 


Of  the  three  main  parts  then  of  a  pulse-tracing,  viz.,  the  percussion 
wave,  the  tidal,  and  the  dicrotic,  the  percussion  wave  is  produced  by 
sudden  and  forcible  contraction  of  the  heart,  perhaps  exaggerated  by  an 
excited  action,  and  may  be  transmitted  much  more  rapidly  than  the  tidal 
wave,  and  so  the  two  may  be  distinct;  frequently,  however,  they  are  in- 
separable. The  dicrotic  wave  may  be  as  great  or  greater  than  the  other 
two. 

According  to  Mahomed,  the  distinctness  of  the  three  waves  depends 
upon  the  following  conditions: — 

The  percussion  wave  is  increased  by: — 1.  Forcible  contraction  of  the 
Heart;  2.  Sudden  contraction  of  the  Heart;  3.  Large  volume  of  blood; 
4.  Fulness  of  vessel;  and  diminished  by  the  reversed  conditions. 

The  tidal  wave  is  increased  by: — 1.   Slow  and  prolonged  contraction 
of  the  Heart;  2.  Large  volume  of  blood;  3.  Comparative  emptiness  of 
vessels;  4.  Diminished  outflow  or  slow  capillary  circu- 
lation; and  diminished  by  the  reversed  conditions. 

The  dicrotic  wave  is  increased  by: — 1.  Sudden  con- 
traction of  the  Heart;  2.  Comparative  emptiness  of 
vessels;  3.  Increased  outflow  or  rapid  capillary  circu- 
lation; 4.  Elasticity  of  the  aorta;  5.  Relaxation  of  mus- 
cular coat;  and  diminished  by  the  reversed  conditions. 

One  very  important  precaution  in  the  use  of  the 
sphygmograph  lies  in  the  careful  regulation  of  the  pres- 
sure. If  the  pressure  be  too  great,  the  characters  of  the 
pulse  may  be  almost  entirely  obscured,  or  the  artery  may 
be  entirely  obstructed,  and  no  tracing  is  obtained;  and 
on  the  other  hand,  if  the  pressure  be  too  slight,  a  very 
small  part  of  the  characters  may  be  represented  on  the 
tracing. 

THE  PRESSURE  OF  THE  BLOOD  WITHIN  THE  ARTERIES 
(PRODUCING  ARTERIAL  TENSION). 

It  will  be  understood  from  the  foregoing  that  the 
arteries  in  a  normal  condition,  are  continually  on  the 
stretch  during  life,  and  in  consequence  of  the  injection 
of  more  blood  at  each  systole  of  the  ventricle  into  the 
elastic  aorta,  this  stretched  condition  is  exaggerated  each  time  the  ventricle 
empties  itself.  This  condition  of  the  arteries  is  due  to  the  pressure  of 
blood  within  them,  because  of  the  resistance  presented  by  the  smaller  ar- 
teries and  capillaries  (peripheral  resistance)  to  the  emptying  of  the  arterial 
system  in  the  intervals  between  the  contractions  of  the  ventricle,  and  is 
called  the  condition  of  arterial  tension.  On  the  other  hand,  it  must  be 
equally  clear  that,  as  the  blood  is  forcibly  injected  into  the  already  full 


ter. 


CIRCULATION    OF    THE    BLOOD.  149 

arteries  against  their  elasticity,  it  must  be  subjected  to  the  pressure  of 
the  arterial  walls,  the  elastic  recoil  sending  on  the  blood  after  the  imme- 
diate effect  of  the  systole  has  passed;  so  that,  when  an  artery  is  cut  across, 
the  blood  is  projected  forward  by  this  force  for  a  considerable  distance; 
at  each  ventricular  systole,  a  jet  of  blood  escaping,  although  the  stream 
does  not  cease  flowing  during  the  diastole. 

The  relations  which  exist  between  the  arteries  and  their  contained 
blood  are  obviously  of  the  utmost  importance  to  the  carrying  on  of  the 
circulation,  and  it  therefore  becomes  necessary  to  be  able  to  gauge  the 


range 

ported  ,, 

to  it;  D,  c,  E,  represent  mercurial  manometer,  a  somewhat  different  form  of  which  is  shown  in  next 

figure. 

alterations  in  blood-pressure  very  accurately.  This  may  be  done  by 
means  of  a  mercurial  manometer  in  the  following  way: — The  short  hori- 
zontal limb  of  this  (Fig.  132,  1)  is  connected,  by  means  of  an  elastic  tube 
and  cannula,  with  the  interior  of  an  artery;  a  solution  of  sodium  or  po- 
tassium carbonate  being  previously  introduced  into  this  part  of  the  appa- 
ratus  to  prevent  coagulation  of  the  blood.  The  blood-pressure  is  thus 
•communicated  to  the  upper  part  of  the  mercurial  column  (2);  and  the 
depth  to  which  the  latter  sinks,  added  to  the  height  to  which  it  rises  in 
the  other  (3),  will  give  the  height  of  the  mercurial  column  which  the 


150 


HAND-BOOK    OF    PHYSIOLOGY. 


blood-pressure  balances;    the  weight   of  the   soda  solution  being  sub- 
tracted. 

For  the  estimation  of  the  arterial  tension  at  any  given  moment,  no 
further  apparatus  than  this,  which  is  called  Poiseuille's  hcemadynamometer, 
is  necessary;  but  for  noting  the  variations  of  pressure  in  the  arterial  sys- 
tem, as  well  as  its  absolute  amount,  the  instrument  is  usually  combined 

with  a  registering  apparatus  and  in  this  form  is 
called  a  kymograph. 

The  kymograph,  invented  by  Ludwig,  is 
composed  of  a  hasmadynamometer,  the  open 
mercurial  column  of  which  supports  a  floating 
piston  and  vertical  rod,  with  short  horizontal 
pen  (Fig.  134).  The  pen  is  adjusted  in  con- 
tact with  a  sheet  of  paper,  which  is  caused  to 
move  at  a  uniform  rate  by  clockwork;  and 
thus  the  up-and-down  movements  of  the  mer- 
curial column,  which  are  communicated  to  the 
rod  and  pen,  are  marked  or  registered  on  the 
moving  paper,  as  in  the  registering  apparatus 
of  the  sphygmograph,  and  minute  variations 
are  graphically  recorded  (Fig.  135). 

For  some  purposes  the  spring  kymograph  of 
Fick  (Fig.  136)  is  preferable  to  the  mercurial 
kymograph.  It  consists  of  a  hollow  C-shaped 
spring,  filled  with  fluid,  the  interior  of  which 
is  brought  into  connection  with  the  interior 
of  an  artery,  by  means  of  a  flexible  metallic  tube  and  cannula.  In 
response  to  the  pressure  transmitted  to  its  interior,  the  spring,  c,  tends 
to  straighten  itself,  and  the  movement  thus  produced  is  communicated 
by  means  of  a  lever,  Z>,  to  a  writing-needle  and  registering  apparatus. 


FIG.  134. — Diagram  of  mercu- 
rial manometer,  a.  Floatiag  rod 
and  pen.  b.  Tube,  which  commu- 
nicates with  a  bottle  containing 
an  alkaline  solution,  c'.  Elastic 
tube  and  cannula,  the  latter  being 
intended  for  insertion  in  an  artery. 


FIG.  135.— Normal  tracing  of  arterial  pressure  in  the  rabbit  obtained  with  the  mercurial  kymo- 
graph. The  smaller  undulations  correspond  with  the  heart  beats;  the  larger  curves  with  the  respir- 
atory movements.  (Burdon-Sanderson.) 

Fig.  137  exhibits  an  ordinary  arterial  pulse-tracing,  as  obtained  by  the 
spring-kymograph . 

From  observations  which  have  been  made  by  means  of  the  mercurial 
manometer,  it  has  been  found  that  the  pressure  of  blood  in  the  carotid  of 
a  rabbit  is  capable  of  supporting  a  column  of  2  to  3^  inches  (50  to  90 


CIRCULATION    OF    THE    BLOOD. 


151 


mm.)  of  mercury,  in  the  dog  4  to  7  inches  (100  to  175  mm.),   in  the 
horse  5  to  8  inches  (150  to  200  mm.),  and  in  man  about  the  same. 

To  measure  the  absolute  amount  of  this  pressure  in  any  artery,  it  is 
necessary  merely  to  multiply  the  area  of  its  transverse  section  by  the 
height  of  the  column  of  mercury  which  is  already  known  to  be  supported 
by  the  blood- pressure  in  any  part  of  the  arterial  system.  The  weight 
of  a  column  of  mercury  thus  found  will  represent  the  pressure  of  the 
blood.  Calculated  in  this  way,  the  blood-pressure  in  the  human  aorta  is 


FIG.  136.— A  form  of  Pick's  Spring  Kymograph,  a,  tube  to  be  connected  with  artery:  c,  hollow 
spring,  the  movement  of  which  moves  6,  the  writing  lever;  e,  screw  to  regulate  height  or  6;  d,  out- 
side protective  spring;  gr,  screw  to  fix  on  the  upright  of  the  support. 

equal  to  4  Ib.  4  oz.  avoirdupois;  that  in  the  aorta  of  the  horse  being 
11  Ib.  9  oz.;  and  that  in  the  radial  artery  at  the  human  wrist  only  4  drs. 
Supposing  the  muscular  power  of  the  right  ventricle  to  be  only  one- 
half  that  of  the  left,  the  blood-pressure  in  the  pulmonary  artery  will  be 
only  2  Ib.  2  oz.  avoirdupois.  The  amounts  above  stated  represent  the 
arterial  tension  at  the  time  of  the  ventricular  contraction. 

The  blood-pressure  is  greatest  in  the  left  ventricle  and  at  the  begin- 
ning of  the  aorta,  and  decreases  toward  the  capillaries.  It  is  greatest  in 
the  arteries  at  the  period  of  the  ventricular  systole,  and  is  least  in  the 
auricles,  during  diastole,  when  the  pressure  there  and  in  the  great  veins 
becomes,  as  we  have  seen,  negative.  The  mean  arterial  pressure  equals 
the  average  of  the  pressures  in  all  the  arteries.  The  pressure  in  the 
veins  is  never  more  than  one-tenth  of  the  pressure  in  the  corresponding 


152  HAND-BOOK    OF    PHYSIOLOGY. 

arteries  and  is  greatest  at  the  time  of  auricular  systole.  There  is  no  peri- 
odic variation  in  venous  pressure,  as  there  is  in  the  arterial,  except  in 
the  great  veins. 


FIG.  137.— Normal  arterial  tracing  obtained  with  Tick's  kymograph  in  the  dog.  (Burdon- 
Sanderson.) 

Variations  of  Blood  Pressure. — Many  circumstances  cause  con- 
siderable variations  in  the  amount  of  the  blood-pressure.  The  following 
are  the  chief: — (1)  Changes  in  the  beat  of  the  Heart;  (2)  Changes  in  the 
Arteries  and  Capillaries;  (3)  'Changes-  due  to  Nerve  Action;  (4)  Changes 
in  the  Blood;  (5)  Respiratory  Changes. 

1.  Changes  in  the  Beat  of  the  Heart. — The  systole  and  diastole  of  the 
muscular  chambers.     The   arterial  tension  increases  during  systole  and 
diminishes  during  diastole.     The  greater  the  frequency,  moreover,  of  the 
heart's  contractions,  the  greater  is  the  blood-pressure,  cceteris  paribus; 
although  this  effect  is  not  constant,  as  it  may  be  compensated  for  by  the 
delivery  into  the  arteries  at  each  beat  of  a  comparatively  small  quantity 
of  blood.     The  greater  the  quantity  of  blood  expelled  from  the  heart  at 
each  contraction  the  greater  is  the  blood-pressure. 

The  quantity  and  quality  of  the  blood  nourishing  the  heart's  substance 
through  the  coronary  arteries  must  exercise  also  a  very  considerable 
influence  upon  its  action,  and  therefore  upon  the  blood-pressure. 

2.  Changes  in  the  Arteries  and  Capillaries. — Variations  in  the  degree 
of  contraction  of  the  smaller  arteries  modify  the  blood -pressure  by  favor- 
ing or  impeding  the  accumulation  of  blood  in  the  arterial  system  which 
follows  every  contraction  of  the  heart;  the  contraction  of  the  arterial 
walls  increasing  the  blood-pressure,  while  their  relaxation  lowers  it. 

3.  Changes  due  to  Nerve  Action. — As  with  the  heart,  so  with  the 
blood-vessels,  the  action  of  the  nervous  system  is  very  important  in  rela- 
tion to  the  blood-pressure;  regulating,  as  it  does,  not  only  the  force,  fre- 
quency, and  length  of  the  heart's  systole,  but  also  the  condition  of  the 
arteries,  both  through  the  central  and  peripheral  vaso- motor  centres.    As 
this  subject  has  not  yet  been  fully  considered  it  will  be  as  well  to  treat  of 
it  here. 

It  is  upon  the  muscular  coat  of  the  arteries  that  the  nervous  system 
exercises  its  influence;  the  elastic  element  possessing,  as  must  be  obvious, 
rather  physical  than  vital  properties.  The  muscular  tissue  in  the  walls 
of  the  vessels  increases  relatively  to  the  other  coats  as  the  arteries  grow 
smaller,  so  that  in  the  smallest  arteries  it  is  developed  out  of  all  propor- 


CIRCULATION    OF    THE    BLOOD.  153 

tion  to  the  other  elements;  in  fact,  in  passing  from  capillary  vessels,  made 
up  as  we  have  seen  of  endothelial  cells  with  a  ground  substance,  the  first 
change  which  occurs  as  the  vessels  become  larger  (on  the  side  of  the 
arteries)  is  the  appearance  of  muscular  fibres.  Thus  the  nervous  system 
is  more  powerful  in  regulating  the  calibre  of  the  smaller  than  of  the  larger 
arteries. 

It  has  been  shown  that  if  the  cervical  sympathetic  nerve  be  divided  in 
a  rabbit,  the  blood-vessels  of  the  corresponding  side  become  dilated.  The 
effect  is  best  seen  in  the  ear,  which  if  held  up  to  the  light  is  seen  to 
become  redder,  and  the  arteries  to  become  larger.  The  whole  ear  is  dis- 
tinctly warmer  than  the  opposite  one.  This  effect  is  produced  by  remov- 
ing the  arteries  from  the  influence  of  the  central  nervous  system,  which 


FIG.  138.— Plethysmograph.  By  means  of  this  apparatus,  the  alteration  in  volume  of  the  arm, 
E,  which  is  enclosed  in  a  glass  tube,  A,  filled  with  fluid,  the  opening  through  which  it  passes  being 
firmly  closed  by  a  thick  gutta  percha  band,  F,  is  communicated  to  the  lever,  D,  and  registered  by  a 
recording  apparatus.  The  fluid  in  A  communicates  with  that  in  B,  the  upper  limit  of  which  is  above 
that  in  A.  The  chief  alterations  in  volume  are  due  to  alteration  in  the  blood  contained  in  the  arm. 
When  the  volume  is  increased,  fluid  passes  out  of  the  glass  cylinder,  and  the  lever,  D,  also  is  raised, 
and  when  a  decrease  takes  place  the  fluid  returns  again  from  B  to  A.  It  will  therefore  be  evident 
that  the  apparatus  is  capable  of  recording  alterations  of  blood-pressure  in  the  arm.  Apparatus 
founded  upon  the  same  principle  have  been  used  for  recording  alterations  in  the  volume  of  the  spleen 
and  kidney. 

influence  usually  passes  down  the  divided  nerve;  for  if  the  peripheral  end 
of  the  divided  nerve  (i.e.,  that  farthest  from  the  brain)  be  stimulated, 
the  arteries  which  were  before  dilated  return  to  their  natural  size,  and 
the  parts  regain  their  primitive  condition.  And,  besides  this,  if  the 
stimulus  which  is  applied  be  too  strong  or  too  long  continued,  the  point 
of  normal  constriction  is  passed,  and  the  vessels  become  much  more  con- 
tracted than  normal.  The  natural  condition,  which  is  somewhere  about 
midway  between  extreme  contraction  and  extreme  dilatation,  is  called  the 
natural  tone  of  an  artery,  and  if  this  be  not  maintained,  the  vessel  is  said 
to  have  lost  tone,  or  if  it  be  exaggerated,  the  tone  is  said  to  be  too  great. 
The  influence  of  the  nervous  system  upon  the  vessels  consists  in  maintain- 
ing a  natural  tone.  The  effects  described  as  having  been  produced  by 
section  of  the  cervical  sympathetic  and  by  subsequent  stimulation  are  not 
peculiar  to  that  nerve,  as  it  has  been  found  that  for  every  part  of  the 


154  HAND-BOOK    OF    PHYSIOLOGY. 

body  there  exists  a  nerve  the  division  of  which  produces  the  same  effects, 
viz.,  dilatation  of  the  arteries;  such  may  be  cited  as  the  case  with  the 
sciatic,  the  splanchnic  nerves,  and  the  nerves  of  the  brachial  plexus: 
when  divided,  dilatation  of  the  blood-vessels  in  the  parts  supplied  by 
them  taking  place.  It  appears,  therefore,  that  nerves  exist  which  have  a 
distinct  control  over  the  vascular  supply  of  a  part. 

These  nerves  are  called  vaso-motor;  or,  since  they  seem  to  run  now 
in  cerebro-spinal  nerves,  now  in  the  sympathetic,  we  speak  of  those 
nerves  as  containing  vaso-motor  fibres,  in  addition  to  the  fibres  which 
have  other  functions. 

Vaso-motor  centres. — Experiments  by  Ludwig  and  others  show 
that  the  vaso-motor  fibres  come  primarily  from  grey  matter  (vaso-motor 
centre)  in  the  interior  of  the  medulla  oblongata,  between  the  calamus 
scriptorius  and  the  corpora  quadrigemina.  Thence  the  vaso-motor  fibres 
pass  down  in  the  interior  of  the  spinal  cord,  and  issuing  with  the  anterior 
roots  of  the  spinal  nerves,  traverse  the  various  ganglia  on  the  pras-vertebral 
cord  of  the  sympathetic,  and,  accompanied  by  branches  from  these 
ganglia,  pass  to  their  destination. 

Secondary  or  subordinate  centres  exist  in  the  spinal  cord,  and  local 
centres  in  various  regions  of  the  body,  and  through  these,  directly  under 
ordinary  circumstances,  vaso-motor  changes  are  also  effected. 

The  influence  exerted  by  the  chief  vaso-motor  centre  is  called  into 
play  in  several  ways,  but  chiefly  by  afferent  (sensory)  stimuli,  and  it  may 
be  exerted  in  two  ways,  either  to  increase  its  usual  action  which  main- 
tains a  medium  tone  of  the  arteries  or  to  diminish  such  action.  This 
afferent  influence  upon  the  centre  may  be  extremely  well  shown  by  the 
action  of  a  nerve  the  existence  of  which  was  demonstrated  by  Cyon  and 
Ludwig,  and  which  is  called  the  depressor,  because  of  its  characteristic 
influence  on  the  blood-pressure. 

Depressor  Nerve. — This  small  nerve  arises,  in  the  rabbit,  from  the 
superior  laryngeal  branch,  or  from  this  and  the  trunk  of  the  pneumogas- 
tric  nerve,  and  after  communicating  with  filaments  of  the  inferior  cervical 
ganglion  proceeds  to  the  heart. 

If  during  an  observation  of  the  blood-pressure  of  a  rabbit  this  nerve 
be  divided,  and  the  central  end  (i.e.,  that  nearest  the  brain)  be  stimu- 
lated, a  remarkable  fall  of  blood-pressure  ensues  (Fig.  139). 

The  cause  of  the  fall  of  blood-pressure  is  found  to  proceed  from  the 
dilatation  of  the  vascular  district  supplied  by  the  splanchnic  nerves,  in 
consequence  of  which  it  holds  a  much  larger  quantity  of  blood  than  usual, 
and  this  very  greatly  diminishes  the  blood  in  the  vessels  elsewhere,  and 
so  materially  affects  the  blood-pressure.  This  effect  of  the  depressor  nerve 
is  presumed  to  prove  that  the  nerve  is  a  means  of  conveying  to  the  vaso- 
motor  centre  indications  of  such  conditions  of  the  heart  as  require  a 
diminution  of  the  tension  in  the  blood-vessels;  as,  for  example,  when  the 


CIRCULATION    OF    THE    BLOOD.  155 

heart  cannot,  with  sufficient  ease,  propel  blood  into  the  already  too  full  or 
too  tense  arteries. 

The  action  of  the  depressor  nerve  illustrates  the  effect  of  afferent  im- 
pulses in  causing  an  inhibition  of  the  vaso-motor  centre  as  regards  its 
action  upon  certain  arteries.  There  exist  other  nerves,  however,  the 
stimulation  of  the  central  end  of  which  causes  a  reverse  action  of  the 
centre,  or,  in  other  words,  increases  its  tonic  influence,  and  by  causing 


FIG.  139.— Tracing  showing  the  effect  on  blood  pressure  of  stimulating  the  central  end  of  the  De- 
pressor nerve  in  the  rabbit.  To  be  read  from  right  to  left.  T,  indicates  the  rate  at  which  the  re- 
cording-surface was  traveling,  the  intervals  correspond  to  seconds;  C,  the  moment  of  entrance  of 
current;  O,  moment  at  which  it  was  shut  off.  The  effect  is  some  time  in  developing  and  lasts  after 
the  current  has  been  taken  off.  The  larger  undulations  are  the  respiratory  nerves;  the  pulse  oscilla- 
tions are  very  small.  (M.  Foster.) 

considerable  constriction  of  certain  arterioles,  either  locally  or  generally, 
increases  the  blood-pressure.  Moreover,  the  effect  of  stimulating  an 
afferent  nerve  may  be  to  dilate  or  constrict  the  arteries  either  generally 
or  in  the  part  supplied  by  the  afferent  nerve;  and  it  is  said  that  stimula- 
tion of  an  afferent  nerve  may  produce  a  kind  of  paradoxical  effect,  causing 
general  vascular  constriction  and  so  general  increase  of  blood-pressure  but 
at  the  same  time  local  dilatation.  This  must  evidently  have  an  immense 
influence  in  increasing  the  flow  of  blood  through  a  part. 

Not  only  may  the  vaso-motor  centre  be  reflexly  affected,  but  it  may 
also  be  affected  by  impulses  proceeding  to  it  from  the  cerebrum,  as  in  the 
case  of  blushing  from  mind  disturbance,  or  of  pallor  from  sudden  fear. 
It  will  be  shown,  too,  in  the  chapter  on  Eespiration  that  the  circulation 
of  deoxygenated  blood  may  directly  stimulate  the  centre  itself. 

Local  Tonic  Centres. — Although  the  tone  of  the  arteries  is  influ- 
enced by  the  centres  in  the  cerebro-spinal  axis,  certain  experiments  point 
out  that  this  is  not  the  only  way  in  wrhich  it  may  be  affected.  Thus  the 
dilatation  which  occurs  after  section  of  the  cervical  sympathetic  in  the 
first  experiment  cited  above,  only  remains  for  a  short  time,  and  is  soon 
followed — although  a  portion  of  the  nerve  may  have  been  removed 
entirely — by  the  vessels  regaining  their  ordinary  calibre;  and  afterward 


156  HAND-BOOK    OF    PHYSIOLOGY. 

local  stimulation,  e.g.,  the  application  of  heat  or  cold,  will  cause  dilatation 
or  constriction.  From  this  it  is  probable  that  there  exists  a  local 
mechanism  distinct  for  each  vascular  area,  and  that  the  effect  produced 
by  the  central  nervous  system  acts  through  it  much  in  the  same  way  as  the 
cardio-inhibitory  centre  in  the  medulla  acts  upon  the  heart  through  the 
ganglia  contained  within  its  muscular  substance. 

Central  impulses  may  inhibit  or  increase  the  action  of  these  local 
centres,  which  may  be  considered  to  be  sufficient  under  ordinary  circum- 
stances to  maintain  the  local  tone  of  the  vessels.  The  observations  upon 
the  functions  of  the  vaso-motor  nerves  appear  to  divide  them  into  four 
classes:  (1)  those  on  division  of  which  dilatation  occurs  for  some  time, 
and  which  on  stimulation  of  their  peripheral  end  produce  constriction; 
(2)  those  on  division  of  which  momentary  dilatation  followed  by  constric- 
tion occurs,  with  dilatation  on  stimulation;  (3)  those  on  division  of  which 
dilatation  is  caused,  which  lasts  for  a  limited  time,  with  constriction  if 
stimulated  at  once,  but  dilatation  if  some  time  is  allowed  to  elapse  before 
the  stimulation  is  applied;  (4)  a  class,  division  of  which  produces  no 
effect  but  which,  on  stimulation,  cause  according  to  their  function  either 
dilatation  or  constriction.  A  good  example  of  this  fourth  class  is  afforded 
by  the  nerves  supplying  the  submaxillary  gland,  viz.,  the  chorda  tympani 
and  the  sympathetic.  When  either  of  these  nerves  is  simply  divided, 
no  change  takes  place  in  the  vessels  of  the  gland;  but  on  stimulating  the 
chorda  tympani  the  vessels  dilate,  and,  on  the  other  hand,  when  the 
sympathetic  is  stimulated  the  vessels  contract.  The  nerves  acting  like 
the  chorda  tympani  in  this  case  are  called  vaso-dilators,  and  those  like 
the  sympathetic  vaso-constrictors.  The  third  class,  which  produce  at  one 
time  dilatation,  at  another  time  constriction,  are  believed  to  contain  both 
kinds  of  vaso-motor  nerve-fibres,  or  to  act  as  dilators  or  contractors 
according  to  the  condition  of  the  local  apparatus.  It  is  probable  that 
these  nerves  act  by  inhibiting  or  augmenting  the  action  of  the  local  nerv- 
ous mechanism  already  referred  to;  and  as  they  are  in  connection  with 
the  central  nervous  system,  it  is  through  this  arrangement  that  that  sys- 
tem is  capable  of  influencing  or  of  maintaining  the  normal  local  tone. 

It  may  also  be  supposed  that  the  local  nerve-centres  themselves  may 
be  directly  affected  by  the  condition  of  blood  nourishing  them. 

The  following  table  may  serve  as  a  summary  of  the  effect  of  the  nerv- 
ous system  upon  the  arteries  and  so  upon  the  blood-pressure: — 

A.  An  increase  of  the  blood-pressure  may  be  produced:— 

(1.)  By  stimulation  of  the  vaso-motor  centre  in  medulla,  either 
a.  Directly,  as  by  carbonated  or  deoxygenated  blood. 
/3.  Indirectly,  by  impressions  descending  from  the  cerebrum, 

e.g.,  in  sudden  pallor. 
y.  Reflexly,  by  stimulation  of  sensory  nerves  anywhere. 


CIRCULATION"  OF    THE    BLOOD.  157 

(2.)  By  stimulation  of  the  centres  in  spinal  cord. 

Possibly  directly  or  indirectly,  certainly  reflexly. 
(3.)  By  stimulation  of  the  local  centres  for  each  vascular  area,  by 

the  vaso-constrictor  nerves,  or  directly  by  means  of  altered 

blood. 

B.  A  decrease  of  the  blood  pressure  may  be  produced:— 

(1.)  By  stimulation  of  the  vaso-motor  centre  in  medulla,  either 
(a.}  Directly,  as  by  oxygenated  or  aerated  blood. 
(p. )  Indirectly,  by  impressions  descending  from  the  cerebrum 

— e.g.,  in  blushing. 

(y.)  Reflexly,  by  stimulation  of  the  depressor  nerve,  and 
consequent  dilatation  of  vessels  of  splanchnic  area,  and 
possibly  by  stimulation  of  other  sensory  nerves,  the  sen- 
sory impulse  being  interpreted  as  an  indication  for 
diminished  blood-pressure. 
(2.)  By  stimulation  of  the  centres  in  spinal  cord.  Possibly 

directly,  indirectly,  or  reflexly. 

(3.)  By  stimulation  of  local  centres  for  each  vascular  area  by  the 
vaso-dilator  nerve,  or  directly  by  means  of  altered  blood. 

4.  Changes  in  the  blood. — a.  As  regards  quantity.  At  first  sight  it 
would  appear  that  one  of  the  easiest  ways  to  diminish  the  blood-pressure 
would  be  to  remove  blood  from  the  vessels  by  bleeding;  it  has  been  found 
by  experiment,  however,  that  although  the  blood-pressure  sinks  whilst 
large  abstractions  of  blood  are  taking  place,  as  soon  as  the  bleeding  ceases 
it  rises  rapidly,  and  speedily  becomes  normal;  that  is  to  say,  unless  so 
large  an  amount  of  blood  has  been  taken  as  to  be  positively  dangerous  to 
life,  abstraction  of  blood  has  little  effect  upon  the  blood-pressure.  The 
rapid  return  to  the  normal  pressure  is  due  not  so  much  to  the  withdrawal 
of  lymph  and  other  fluids  from  the  body  into  the  blood,  as  was  formerly 
supposed,  as  to  the  regulation  of  the  peripheral  resistance  by  the  vaso- 
motor  nerves;  in  other  words,  the  small  arteries  contract,  and  in  so  doing 
maintain  pressure  on  the  blood  and  favor  its  accumulation  in  the  arterial 
system.  This  is  due  to  the  stimulation  of  the  vaso-motor  centre  from 
diminution  of  the  supply  of  blood,  and  therefore  of  oxygen.  The  failure 
of  the  blood-pressure  to  return  to  normal  in  the  too  great  abstraction 
must  be  taken  to  indicate  a  condition  of  exhaustion  of  the  centre,  and 
consequently  of  want  of  regulation  of  the  peripheral  resistance.  In  the 
same  way  it  might  be  thought  that  injection  of  blood  into  the  already 
pretty  full  vessels  would  be  at  once  followed  by  rise  in  the  blood-pressure, 
and  this  is  indeed  the  case  up  to  a  certain  point — the  pressure  does  rise, 
but  there  is  a  limit  to  the  rise.  Until  the  amount  of  blood  injected 
equals  about  2  to  3  per  cent,  of  the  body  weight  the  pressure  continues  to 
rise  gradually;  but  if  the  amount  exceed  this  proportion,  the  rise  does  not 
continue.  In  this  case  therefore,  as  in  the  opposite  when  blood  is  ab- 


158  HAND-BOOK  OF"  PHYSIOLOGY. 

stracted,  the  vaso motor  apparatus  must  counteract  the  great  increase  of 
pressure  by  dilating  the  small  vessels,  and  so  diminishing  the  peripheral 
resistance,  for  after  each  rise  there  is  a  partial  fall  of  pressure;  and  after 
the  limit  is  reached  the  whole  of  the  injected  blood  displaces,  as  it  were, 
an  equal  quantity  which  passes  into  the  small  veins,  and  remains  within 
them.  It  should  be  remembered  that  the  veins  are  capable  of  holding 
the  whole  of  the  blood  of  the  body. 

The  amount  of  blood  supplied  to  the  heart  both  to  its  substance  and 
to  its  chambers,  has  a  marked  effect  upon  the  blood-pressure. 

1).  As  regards  quality.  The  quality  of  the  blood  supplied  to  the  heart 
has  a  distinct  effect  upon  its  contraction,  as  too  watery  or  too  little  oxy- 
genated blood  must  interfere  with  its  action.  Thus  it  appears  that  blood 
containing  certain  substances  affects  the  peripheral  resistance  by  acting 
upon  the  muscular  fibres  of  the  arterioles  themselves  or  upon  the  local 
centres,  and  so  altering  directly,  as  it  were,  the  calibre  of  the  vessels. 

5.  Respiratory  changes  affecting  the  blood-pressure  will  be  considered 
in  the  next  Chapter. 

CIRCULATION  IN  THE  CAPILLARIES. 

When  seen  in  any  transparent  part  of  a  living  adult  animal  by  means 
of  the  microscope  (Fig.  140)  the  blood  flows  with  a  constant  equable  mo- 
tion; the  red  blood-corpuscles  moving  along,  mostly  in  single  file,  and 
bending  in  various  ways  to  accommodate  themselves  to  the  tortuous  course 

of  the  capillary,  but  instantly  recovering  their 
normal  outline  on  reaching  a  wider  vessel. 

It  is  in  the  capillaries  that  the  chief  resist- 
ance is  offered  to  the  progress  of  the  blood; 
for  in  them  the  friction  of  the  blood  is  greatly 
increased  by  the  enormous  multiplication  of 
the  surface  with  which  it  is  brought  in  con- 
tact. 

At  the  circumference  of  the  stream  in  the 
larger  capillaries,  but  chiefly  in  the  small  arte- 
FIG.  140.— capillaries  (o  in  the    ries  and  veins,  in  contact  with  the  walls  of 

web  of  the  frog  s  foot  connecting  a 

small  artery  (A)  with  a  small  vein  v    the  vessel,   and   adhering  to  them,  there   is 

(after  Allen  Thomson).  /  .  °. 

a  layer  of  liquor  sangumis  which  appears  to 

be  motionless.  The  existence  of  this  still  layer,  as  it  is  termed,  is 
inferred  both  from  the  general  fact  that  such  an  one  exists  in  all  fine 
tubes  traversed  by  fluid,  and  from  what  can  be  seen  in  watching  the  move- 
ments of  the  blood-corpuscles.  The  red  corpuscles  occupy  the  middle  of 
the  stream  and  move  with  comparative  rapidity;  the  colorless  lymph-cor- 
puscles run  much  more  slowly  by  the  walls  of  the  vessel;  while  next  to 
the  wall  there  is  often  a  transparent  space  in  which  the  fluid  appears  to 


CIRCULATION    OF    THE    BLOOD. 


159 


be  at  rest;  for  if  any  of  tne  corpuscles  happen  to  be  forced  within  it,  they 
move  more  slowly  than  before,  rolling  lazily  along  the  side  of  the  vessel, 
and  often  adhering  to  its  wall.  Part  of  this  slow  movement  of  the  pale 
corpuscles  and  their  occasional  stoppage  may  be  due  to  their  having  a 
natural  tendency  to  adhere  to  the  walls  of  the  vessels.  Sometimes,  in- 
deed, when  the  motion  of  the  blood  is  not  strong,  many  of  the  white  cor- 
puscles collect  in  a  capillary  vessel,  and  for  a  time  entirely  prevent  the 
passage  of  the  red  corpuscles. 

Intermittent  flow  in  the  Capillaries. — When  the  peripheral  re- 
sistance is  greatly  diminished  by  the  dilatation  of  the  small  arteries  and 
capillaries,  so  much  blood  passes  on  from  the  arteries  into  the  capillaries 
at  each  stroke  of  the  heart,  that  there  is  not  sufficient  remaining  in  the 
arteries  to  distend  them.  'Thus,  the  intermittent  current  of  the  ventric- 
ular systole  is  not  converted  into  a  continuous  stream  by  the  elasticity 
of  the  arteries  before  the  capillaries  are  reached;  and  so  intermittency  of 
the  flow  occurs  in  capillaries  and  veins  and  a  pulse  is  produced.  The 
same  phenomenon  may  occur  when  the  arteries  become  rigid  from  disease, 
and  when  the  beat  of  the  heart  is  so  slow  or  so  feeble 
that  the  blood  at  each  cardiac  systole  has  time  to  pass 
on  to  the  capillaries  before  the  next  stroke  occurs,  the 
amount  of  blood  sent  at  each  stroke  being  insufficient 
to  properly  distend  the  elastic  arteries. 

Diapedesis  of  Blood  Corpuscles. — Until  with- 
in the  last  few  years  it  has  been  generally  supposed 
that  the  occurrence  of  any  transudation  from  the  in- 
terior of  the  capillaries  into  the  midst  of  the  sur- 
rounding tissues  was  confined,  in  the  absence  of 
injury,  strictly  to  the  fluid  part  of  the  blood;  in  other 
words,  that  the  corpuscles  could  not  escape  from  the 
circulating  stream,  unless  the  wall  of  the  containing 
blood-vessel  were  ruptured.  It  is  true  that  an  Eng- 
lish physiologist,  Augustus  Waller,  affirmed,  in  1846, 
that  he  had  seen  blood-corpuscles,  both  red  and  white, 
pass  bodily  through  the  wall  of  the  capillary  vessel 
in  which  they  were  contained  (thus  confirming  what 
had  been  stated  a  short  time  previously  by  Addison) ; 
and  that,  as  no  opening  could  be  seen  before  their 
escape,  so  none  could  be  observed  afterward — so 
rapidly  was  the  part  healed.  But  these  observations  did  not  attract 
much  notice  until  the  phenomena  of  escape  of  the  blood-corpuscles  from 
the  capillaries  and  minute  veins,  apart  from  mechanical  injury,  were  re- 
discovered by  Professor  Cohnheim  in  1867. 

Cohnheim's  experiment  demonstrating  the  passage  of  the  corpuscles 
through  the  wall  of  the  blood-vessel,  is  performed  in  the  following  man- 


Fio.  141.— A  large  cap- 
illary from  the  frog^s 
mesentery  eight  hours 
after  irritation  had  been 
set  up,  showing  emigra- 
tion of  leucocytes,  a, 
Cells  in  the  act  of  trav- 
ersing the  capillary 
6,  some  already 
(Frey.) 


wall; 


160  HAND-BOOK    OF    PHYSIOLOGY. 

ner.  A  frog  is  urarized,  that  is  to  say,  paralysis  is  produced  by  inject- 
ing under  the  skin  a  minute  quantity  of  the  poison  called  urari;  and  the 
abdomen  having  been  opened,  a  portion  of  small  intestine  is  drawn  out, 
and  its  transparent  mesentery  spread  out  under  a  microscope.  After  a 
variable  time,  occupied  by  dilatation,  following  contraction  of  the  minute 
vessels  and  accompanying  quickening  of  the  blood-stream,  there  ensues  a 
retardation  of  the  current,  and  blood-corpuscles,  both  red  and  white, 
begin  to  make  their  way  through  the  capillaries  and  small  veins. 

"Simultaneously  with  the  retardation  of  the  blood-stream,  the  leu- 
cocytes, instead  of  loitering  here  and  there  at  the  edge  of  the  axial  cur- 
rent, begin  to  crowd  in  numbers  against  the  vascular  wall.  In  this  way 
the  vein  becomes  lined  with  a  continuous  pavement  of  these  bodies,  which 
remain  almost  motionless,  notwithstanding  that  the  axial  current  sweeps 
by  them  as  continuously  as  before,  though  with  abated  velocity.  Now  is 
the  moment  at  which  the  eye  must  be  fixed  on  the  t  outer  contour  of  the 
vessel,  from  which,  here  and  there,  minute,  colorless,  button-shaped  ele- 
vations spring,  just  as  if  they  were  produced  by  budding  out  of  the  wall 
of  the  vessel  itself.  The  buds  increase  gradually  and  slowly  in  size,  until 
each  assumes  the  form  of  a  hemispherical  projection,  of  width  correspond- 
ing to  that  of  the  leucoc}^te.  Eventually  the  hemisphere  is  converted  into 
a  pear-shaped  body,  the  small  end  of  which  is  still  attached  to  the  surface 
of  the  vein,  while  the  round  part  projects  freely.  Gradually  the  little 
mass  of  protoplasm  removes  itself  further  and  further  away,  and,  as  it 
does  so,  begins  to  shoot  out  delicate  prongs  of  transparent  protoplasm  from 
its  surface,  in  nowise  differing  in  their  aspect  from  the  slender  thread  by 
which  it  is  still  moored  to  the  vessel.  Finally  the  thread  is  severed  and 
the  process  is  complete."  (Burdon  Sanderson.) 

The  process  of  diapedesis  of  the  red  corpuscles,  which  occurs  under 
circumstances  of  impeded  venous  circulation,  and  consequently  in- 
creased blood-pressure,  resembles  closely  the  migration  of  the  leuco- 
cytes, with  the  exception  that  they  are  squeezed  through  the  wall  of 
the  vessel,  and  do  not,  like  them,  work  their  way  through  by  amoeboid 
movement. 

Various  explanations  of  these  remarkable  phenomena  have  been  sug- 
gested. Some  believe  that  minute  openings  (stigmata  or  pseudo  stomata) 
between  contiguous  endothelial  cells  (p.  133)  provide  the  means  of  escape 
for  the  blood-corpuscles.  But  the  chief  share  in  the  process  is  to  be  found 
in  the  vital  endowments  with  respect  to  mobility  and  contraction  of  the 
parts  concerned — both  of  the  corpuscles  (Bastian)  and  the  capillary  wall 
(Strieker).  Burdon-Sanderson  remarks,  "the  capillary  is  not  a  dead 
conduit,  but  a  tube  of  living  protoplasm.  There  is  no  difficulty  in  un- 
derstanding how  the  membrane  may  open  to  allow  the  escape  of  leucocytes, 
and  close  again  after  they  have  passed  out;  for  it  is  one  of  the  most  strik- 
ing peculiarities  of  contractile  substance  that  when  two  parts  of  the  same 


CIRCULATION    OF    THE    BLOOD.  161 

mass  are  separated,  and  again  brought  into  contact,  they  melt  together  as 
if  they  had  not  been  severed/' 

Hitherto,  the  escape  of  the  corpuscles  from  the  interior  of  the  blood- 
vessels into  the  surrounding  tissues  has  been  studied  chiefly  in  connection 
with  pathology.  But  it  is  impossible  to  say,  at  present,  to  what  degree 
the  discovery  may  not  influence  all  present  notions  regarding  the  nutrition 
of  the  tissues,  even  in  health. 

Vital  Capillary  Force. — The  circulation  through  the  capillaries  must, 
of  necessity,  b  ^  largely  influenced  by  that  which  occurs  in  the  vessels  on 
either  side  of  them — in  the  arteries  or  the  veins;  their  intermediate  posi- 
tion causing  them  to  feel  at  once,  so  to  speak,  any  alteration  in  the  size 
or  rate  of  the  arterhl  or  venous  blood-stream.  Thus,  the  apparent  con- 
traction of  the  capillaries,  on  the  application  of  certain  irritating  sub- 
stances, and  during  fear,  and  their  dilatation  in  blushing,  may  be  referred 
to  the  action  of  the  small  arteries,  rather  than  to  that  of  the  capillaries 
themselves.  But  largely  as  the  capillaries  are  influenced  by  these,  and  by 
the  conditions  of  the  parts  which  surround  and  support  them,  their  own 
endowments  must  not  be  disregarded.  They  must  be  looked  upon,  not  as 
mere  passive  channels  for  the  passage  of  blood,  but  as  possessing  endow- 
ments of  their  own  (vital  capillary  force),  in  relation  to  the  circulation. 
The  capillary  wall  is  actively  living  and  contractile;  and  there  is  no  reason 
to  doubt  that,  as  such,  it  must  have  an  important  influence  in  connection 
with  the  blood-current. 

Blood-Pressure  in  the  Capillaries.— From  observations  upon  the 
web  of  the  frog's  foot,  the  tongue  and  mesentery  of  the  frog,  the  tails  of 
newts,  and  small  fishes  (Roy  and  Brown),  as  well  as  upon  the  skin  of  the 
finger  behind  the  nail  (Kries),  by  careful  estimation  of  the  amount  of 
pressure  required  to  empty  the  vessels  of  blood  under  various  conditions,, 
it  appears  that  the  blood-pressure  is  subject  to  variations  in  the  capillaries, 
apparently  following  the  variations  of  that  of  the  arteries;  and  that  up  to 
a  certain  point,  as  the  extravascular  pressure  is  increased,  so  does  the  pulse 
in  the  arterioles,  capillaries,  and  venules  become  more  and  more  evident. 
The  pressure  in  the  first  case  (web  of  the  frog's  foot)  has  been  found  to 
be  equal  to  about  14  to  20  mm.  of  mercury;  in  other  experiments  to  be 
equal  to  about  \  to  I-  of  the  ordinary  arterial  pressure. 

THE  CIKCULATION  IN  THE  VEINS. 

The  blood-current  in  the  veins  is  maintained  by  the  slight  vis  a  tergo 
remaining  of  the  contraction  of  the  left  ventricle.  Very  effectual  assist- 
ance, however,  to  the  flow  of  blood  is  afforded  by  the  action  of  the  muscles 
capable  of  pressing  on  such  veins  as  have  valves. 

The  effect  of  such  muscular  pressure  may  be  thus  explained.  When 
pressure  is  applied  to  any  part  of  a  vein,  and  the  current  of  blood  in  it  is 
VOL.  I.— 11. 


162  HAND-BOOK    OF    PHYSIOLOGY. 

obstructed,  the  portion  behind  the  seat  of  pressure  becomes  swollen  and 
distended  as  far  back  as  to  the  next  pair  of  valves.  These,  acting  like  the 
semiluiiar  valves  of  the  heart,  and  being,  like  them,  inextensible  both  in 
themselves  and  at  their  margins  of  attachment,  do  not  follow  the  vein  in 
its  distension,  but  are  drawn  out  toward  the  axis  of  the  canal.  Then,  if 
the  pressure  continues  on  the  vein,  the  compressed  blood,  tending  to  move 
equally  in  all  directions,  presses  the  valves  down  into  contact  at  their 
free  edges,  and  they  close  the  vein  and  prevent  regurgitation  of  the  blood. 
Thus,  whatever  force  is  exercised  by  the  pressure  of  the  muscles  on  the 
veins,  is  distributed  partly  in  pressing  the  blood  onward  in  the  proper 
course  of  the  circulation,  and  partly  in  pressing  it  backward  and  closing 
the  valves  behind  (Fig.  128,  A  and  B). 

The  circulation  might  lose  as  much  as  it  gains  by  such  compression  of 
the  veins,  if  it  were  not  for  the  numerous  anastomoses  by  which  they 
communicate,  one  with  another;  for  through  these,  the  closing  up  of  the 
venous  channel  by  the  backward  pressure  is  prevented  from  being  any 
serious  hindrance  to  the  circulation,  since  the  blood,  of  which  the  onward 
course  is  arrested  by  the  closed  valves,  can  at  once  pass  through  some 
anastomosing  channel,  and  proceed  on  its  way  by  another  vein.  Thus, 
therefore,  the  effect  of  muscular  pressure  upon  veins  which  have  valves, 
is  turned  almost  entirely  to  the  advantage  of  the  circulation;  the  pressure 
of  the  blood  onward  is  all  advantageous,  and  the  pressure  of  the  blood  back- 
ward is  prevented  from  being  a  hindrance  by  the  closure  of  the  valves  and 
the  anastomoses  of  the  veins. 

The  effects  of  such  muscular  pressure  are  well  shown  by  the  accelera- 
tion of  the  stream  of  blood  when,  in  venesection,  the  muscles  of  the  fore- 
arm are  put  in  action,  and  by  the  general  acceleration  of  the  circulation 
during  active  exercise:  and  the  numerous  movements  which  are  continu- 
ally taking  place  in  the  body  while  awake,  though  their  single  effects  may 
be  less  striking,  must  be  an  important  auxiliary  to  the  venous  circulation. 
Yet  they  are  not  essential;  for  the  venous  circulation  continues  unim- 
paired in  parts  at  rest,  in  paralyzed  limbs,  and  in  parts  in  which  the  veins 
are  not  subject  to  any  muscular  pressure. 

Rhythmical  Contraction  of  Veins. — In  the  web  of  the  bat's  wing, 
the  veins  are  furnished  with  valves,  and  possess  the  remarkable  property  of 
rhythmical  contraction  and  dilatation,  whereby  the  current  of  blood  within 
them  is  distinctly  accelerated.  ( Wharton  Jones. )  The  contraction  occurs, 
on  an  average,  about  ten  times  in  a  minute;  the  existence  of  valves  pre- 
venting regurgitation,  the  entire  effect  of  the  contractions  was  auxiliary 
to  the  onward  current  of  blood.  Analogous  phenomena  have  been  fre- 
qu3iitly  observed  in  other  animals. 

Blood-Pressure  in  the  Veins. — The  blood-pressure  gradually  falls 
as  we  proceed  from  the  heart  to  the  arteries,  from  these  to  the  capillaries, 
.and  thence  along  the  veins  to  the  right  auricle.  The  blood-pressure  in 


CIRCULATION    OF    THE    BLOOD.  163 

the  veins  is  nowhere  very  great,  but  is  greatest  in  the  small  veins,  while 
in  the  large  veins  toward  the  heart  the  pressure  becomes  negative,  or,  in 
other  words,  when  a  vein  is  put  in  connection  with  a  mercurial  manometer 
the  mercury*  will  fall  in  the  area  furthest  away  from  the  vein  and  will  rise 
in  the  area  nearest  the  vein,  having  a  tendency  to  suck  in  rather  than  to 
push  forward.  In  the  veins  in  the  neck  this  tendency  to  suck  in  air  is 
especially  marked,  and  is  the  cause  of  death  in  some  operations  in  that 
region.  The  amount  of  pressure  in  the  brachial  vein  is  said  to  support 
9  mm.  of  mercury,  whereas  the  pressure  in  the  veins  of  the  neck  is  about 
equal  to  a  negative  pressure  of  — 3  to  —8  mm. 

The  variations  of  venous  pressure  during  systole  and  diastole  of  the 
heart  are  very  slight,  and  a  distinct  pulse  is  seldom  seen  in  veins  except 
under  very  extraordinary  circumstances. 

The  formidable  obstacle  to  the  upward  current  of  the  blood  in  the 
Teins  of  the  trunk  and  extremities  in  the  erect  posture  supposed  to  be  pre- 
sented by  the  gravitation  of  the  blood,  has  no  real  existence,  since  the 
pressure  exercised  by  the  column  of  blood  in  the  arteries,  will  be  always 
sufficient  to  support  a  column  of  venous  blood  of  the  same  height  as  itself: 
the  two  columns  mutually  balancing  each  other.  Indeed,  so  long  as 
both  arteries  and  veins  contain  continuous  columns  of  blood,  the  force  of 
gravitation,  whatever  be  the  position  of  the  body,  can  have  no  power  to 
move  or  resist  the  motion  of  any  part  of  the  blood  in  any  direction.  The 
lowest  blood-vessels  have,  of  course,  to  bear  the  greatest  amount  of  pres- 
sure; the  pressure  on  each  part  being  dire'ctly  proportionate  to  the  height 
of  the  column  of  blood  above  it:  hence  their  liability  to  distension.  But 
this  pressure  bears  equally  on  both  arteries  and  veins,  and  cannot  either 
move,  or  resist  the  motion  of,  the  fluid  they  contain,  so  long  as  the  col- 
umns of  fluid  are  of  equal  height  in  both,  and  continuous. 

» 
VELOCITY  OF  THE  CIRCULATION. 

The  velocity  of  the  blood-current  at  any  given  point  in  the  various 
divisions  of  the  circulatory  system  is  inversely  proportional  to  their 
sectional  area  at  that  point.  If  the  sectional  area  of  all  the  branches 
of  a  vessel  united  were  always  the  same  as  that  of  the  vessel  from  which 
they  arise,  and  if  the  aggregate  sectional  area  of  the  capillary  vessels 
were  equal  to  that  of  the  aorta,  the  mean  rapidity  of  the  blood's  motion 
in  the  capillaries  would  be  the  same  as  in  the  aorta  and  largest  arteries; 
and  if  a  similar  correspondence  of  capacity  existed  in  the  veins  and 
arteries,  there  would  be  an  equal  correspondence  in  the  rapidity  of  the 
circulation  in  them.  But  the  arterial  and  venous  systems  may  be  rep- 
resented by  two  truncated  cones  with  their  apices  directed  toward  the 
heart;  the  area  of  their  united  base  (the  sectional  area  of  the  capillaries) 
being  400 — 800  times  as  great  as  that  of  the  truncated  apex  representing 


164 


HAND-BOOK    OF    PHYSIOLOGY. 


the  aorta.     Thus  the  velocity  of  blood  in  the  capillaries  is  at  least  j^-g-  of 
that  in  the  aorta. 

Velocity  in  the  Arteries. — The  velocity  of  the  stream  of  blood  is 
greater  in  the  arteries  than  in  any  other  part  of  the  circulatory  system, 
and  in  them  it  is  greatest  in  the  neighborhood  of  the  heart,  and  during 
the  ventricular  systole;  the  rate  of  movement  diminishing  during  the  dias- 
tole of  the  ventricles,  and  in  the  parts  of  the  arterial  system  most  distant 
from  the  heart.  Chauveau  has  estimated  the  rapidity  of  the  blood- 
stream in  the  carotid  of  the  horse  at  over  20  inches  per  second  during  the 
heart's  systole,  and  nearly  6  inches  during  the  diastole  (520 — 150  mm.). 

Estimation  of  the  Velocity. — Various  instruments  have  been  devised 
for  measuring  the  velocity  of  the  blood-stream  in  the  arteries.     Ludwig's 
f  "ffiromuhr"  (Fig.  142)  consists  of  a  U-shaped  glass  tube 

dilated  at  a  and  #',  and  whose  extremities,  Ji  and  i,  are 
of  known  calibre.  The  bulbs  can  be  filled  by  a  common 
opening  at  k.  The  instrument  is  so  contrived  that  at  b 
and  V  the  glass  part  is  firmly  fixed  into  metal  cylinders, 
which  are  fixed  into  a  circular  horizontal  table,  c  c' ,  capa- 
ble of  horizontal  movement  on  a  similar  table  d  d'  about 
the  vertical  axis  marked  in  figure  by  a  dotted  line.  The 
opening  in  c  c',  when  the  instrument  is  in  position,  as  in 
Fig.,  corresponds  exactly  with  those  in  d  d'\  but  if  c  cr 
be  turned  at  right  angles  to  its  present  position,  there 
is  no  communication  between  Ji  and  a,  and  i  and  a', 
but  h  communicates  directly  with  i\  and  if  turned 
through  two  right  angles ,  c'  communicates  with  d,  and 
c  with  d' ,  and  there  is  no  direct  connection  between  h 
and  i.  The  experiment  is  performed  in  the  following 
way: — The  artery  to  be  experimented  upon  is  divided 
and  connected  with  two  cannulse  and  tubes  which  fit  it 
accurately  with  h  and  i — Ji  the  central  end,  and  i  the 
peripheral;  the  bulb  a  is  filled  with  olive  oil  up  to  a  point 
rather  lower  than  k,  and  a'  and  the  remainder  of  a  is  filled  with  defibri- 
nated  blood;  the  tube  on  k  is  then  carefully  clamped;  the  tubes  d  and 
d'  are  also  filled  with  defibrinated  blood.  When  everything  is  ready,  the 
blood  is  allowed  to  flow  into  a  through  Ji,  and  it  pushes  before  it  the  oil, 
and  that  the  defibrinated  blood  into  the  artery  through  i,  and  replaces 
it  in  #';  when  the  blood  reaches  the  former  level  of  the  oil  in  a,  the  disc 
c.c'  is  turned  rapidly  through  two  right  angles,  and  the  blood  flowing 
through  d  into  a'  again  displaces  the  oil  which  is  driven  into  a.  This 
is  repeated  several  times,  and  the  duration  of  the  experiment  noted. 
The  capacity  of  a  and  a'  is  known;  the  diameter  of  the  artery  is  also 
known  by  its  corresponding  with  the  cannulae  of  known  diameter,  and  as 
the  number  of  times  a  has  been  filled  in  a  given  time  is  known,  the 
velocity  of  the  current  can  be  calculated. 


FIG.  142.— Ludwig's 
Stromuhr. 


CIRCULATION    OF    THE    BLOOD. 


165 


Chauveau's  instrument  (Fig.  143)  consists  of  a  thin  brass  tube,  #,  in 
one  side  of  which  is  a  small  perforation  closed  by  thin  vulcanized  india- 
rubber.  Passing  through  the  rubber  is  a  fine  lever,  one  end  of  which, 
slightly  flattened,  extends  into  the  lumen  of  the  tube,  while  the  other 
moves  over  the  face  of  a  dial.  The  tube  is  inserted  into  the  interior  of 


FIQ.  143.— Diagram  of  Chauveau's  Instrument,  a.  Brass  tube  for  introduction  into  the  lumen  of 
the  artery,  and  containing  an  index-needle,  which  passes  through  the  elastic  membrane  in  its  side, 
and  moves  by  the  impulse  of  the  blood-current,  c.  Graduated  scale,  for  measuring  the  extent  of  the 
oscillations  of  the  needle. 

an  artery,  and  ligatures  applied  to  fix  it,  so  that  the  movement  of  the 
blood  may,  in  flowing  through  the  tube,  be  indicated  by  the  movement  of 
the  outer  extremity  of  the  lever  on  the  face  of  the  dial. 

The  Hcematochometer  of  Vierordt,  and  the  instrument  of  Lortet, 
resemble  in  principle  that  of  Chauveau. 

Velocity  in  the  Capillaries. — the  observations  of  Hales,  E.  H. 
Weber,  and  Valentin  agree  very  closely  as  to  the  rate  of  the  ftood-current 
in  the  capillaries  of  the  frog;  and  the  mean  of  their  estimates  gives  the 
velocity  of  the  systemic  capillary  circulation  at  about  one  inch  (25  mm.) 
per  minute.  The  velocity  in  the  capillaries  of  warm-blooded  animals  is 
greater.  In  the  dog  -^  to  T-§-JJ-  inch  ( '5  to  *75  mm. )  a  second.  This  may 
seem  inconsistent  with  the  facts  which  show  that  the  whole  circulation  is 
accomplished  in  about  half  a  minute.  But  the  whole  length  of  capillary 
vessels,  through  which  any  given  portion  of  blood  has  to  pass,  probably 
does  not  exceed  from  -^ th  to  -^th  Of  an  inch  ( '5  mm. ) ;  and  therefore 
the  time  required  for  each  quantity  of  blood  to  traverse  its  own  appointed 
portion  of  the  general  capillary  system  will  scarcely  amount  to  a  second. 

Velocity  in  the  Veins. — The  velocity  of  the  blood  is  greater  in  the 
veins  than  in  the  capillaries,  but  less  than  in  the  arteries:  this  fact 
depending  upon  the  relative  capacities  of  the  arterial  and  venous  systems. 
If  an  accurate  estimate  of  the  proportionate  areas  of  arteries  and  the  veins 
corresponding  to  them  could  be  made,  we  might,  from  the  velocity  of  the 
arterial  current,  calculate  that  of  the  venous.  A  usual  estimate  is,  that 
the  capacity  of  the  veins  is  about  twice  or  three  times  as  great  as  that  of 
the  arteries,  and  that  the  velocity  of  the  blood's  motion  is,  therefore, 


166  HAND-BOOK    OF    PHYSIOLOGY. 

about  twice  or  three  times  as  great  in  the  arteries  as  in  the  veins,  8  inches 
(about  200  mm.)  a  second.  The  rate  at  which  the  blood  moves  in  the 
veins  gradually  increases  the  nearer  it  approaches  the  heart,  for  the  sec- 
tional area  of  the  venous  trunks,  compared  with  that  of  the  branches 
opening  into  them,  becomes  gradually  less  as  the  trunks  advance  toward 
the  heart. 

Velocity  of  the  Circulation  as  a  whole.— It  would  appear  that  a 
portion  of  blood  can  traverse  the  entire  course  of  the  circulation,  in  the 
horse,  in  half  a  minute.  Of  course  it  would  require  longer  to  traverse 
the  vessels  of  the  most  distant  part  of  the  extremities  than  to  go  through 
those  of  the  neck:  but  taking  an  average  length  of  vessels  to  be  traversed, 
and  assuming,  as  we  may,  that  the  movement  of  blood  in  the  human 
subject  is  not  slower  than  in  the  horse,  it  may  be  concluded  that  half  a 
minute  represents  the  average  rate. 

Satisfactory  data  for  these  estimates  are  afforded  by  the  results  of 
experiments  to  ascertain  the  rapidity  with  which  poisons  introduced  into 
the  blood  are  transmitted  from  one  part  of  the  vascular  system  to 
another.  The  time  required  for  the  passage  of  a  solution  of  potassium 
ferrocyanide,  mixed  with  the  blood,  from  one  jugular  vein  (through  the 
right  side  of  the  heart,  the  pulmonary  vessels,  the  left  cavities  of  the 
heart,  and  the  general  circulation)  to  the  jugular  vein  of  the  opposite 
side,  varies  from  twenty  to  thirty  seconds.  The  same  substance  was 
transmitted  from  the  jugular  vein  to  the  great  saphena  in  twenty  seconds; 
from  the  jugular  vein  to  the  m'asseteric  artery,  in  between  fifteen  and 
thirty  seconds;  to  the  facial  artery,  in  one  experiment,  in  between  ten 
and  fifteen  seconds;  in  another  experiment  in  between  twenty  and  twenty- 
five  seconds;  in  its  transit  from  the  jugular  vein  to  the  metatarsal  artery, 
it  occupied  between  twenty  and  thirty  seconds,  and  in  one  instance  more 
than  forty  seconds.  The  result  was  nearly  the  same  whatever  was  the 
rate  of  the  heart's  action. 

In  all  these  experiments,  it  is  assumed  that  the  substance  injected 
moves  with  the  blood,  and  at  the  same  rate,  and  does  not  move  from  one 
part  of  the  organs  of  circulation  to  another  by  diffusing  itself  through  the 
blood  or  tissues  more  quickly  than  the  blood  moves.  The  assumption  is 
sufficiently  probable,  to  be  considered  nearly  certain,  that  the  times  above 
mentioned,  as  occupied  in  the  passage  of  the  injected  substances,  are 
those  in  which  the  portion  of  blood,  into  which  each  was  injected,  was 
carried  from  one  part  to  another  of  the  vascular  system. 

Another  mode  of  estimating  the  general  velocity  of  the  circulating 
blood,  is  by  calculating  it  from  the  quantity  of  blood  supposed  to  be  con- 
tained in  the  body,  and  from  the  quantity  which  can  pass  through  the 
heart  in  each  of  its  actions.  But  the  conclusions  arrived  at  by  this 
method  are  less  satisfactory.  For  the  estimates  both  of  the  total  quantity 
of  blood,  and  of  the  capacity  of  the  cavities  of  the  heart,  have  as  yet  only 


CIRCULATION    OF    THE    BLOOD.  167 

approximated  to  the  truth.  Still  the  most  careful  of  the  estimates  thus 
made  accord  very  nearly  with  those  already  mentioned;  and  it  may  be 
assumed  that  the  blood  may  all  pass  through  the  heart  in  from  twenty- 
five  to  fifty  seconds. 

Peculiarities  of  the  Circulation  in  Different  Parts.— The  most 
remarkable  peculiarities  attending  the  circulation  of  blood  through  differ- 
ent organs  are  observed  in  the  cases  of  the  brain,  the  erectile  organs,  the 
lungs,  the  liver,  and  the  kidney. 

1.  In  the  Brain. — For  the  due  performance  of  its  functions,  the  brain 
requires  a  large  supply  of  blood.  This  object  is  effected  through  the 
number  and  size  of  its  arteries,  the  two  internal  carotids,  and  the  two 
vertebrals.  It  is  further  necessary  that  the  force  with  which  this  blood  is 
sent  to  the  brain  should  be  less,  or  at  least  should  be  subject  to  less  vari- 
ation from  external  circumstances  than  it  is  in  other  parts,  and  so  the 
large  arteries  are  very  tortuous  and  anastomose  freely  in  the  circle  of 
AVillis,  which  thus  insures  that  the  supply  of  blood  to  the  brain  is  uni- 
form, though  it  may  by  an  accident  be  diminished,  or  in  some  way 
changed,  through  one  or  more  of  the  principal  arteries.  The  transit  of 
the  large  arteries  through  bone,  especially  the  carotid  canal  of  the  tem- 
poral bone,  may  prevent  any  undue  distension;  and  uniformity  of  supply 
is  further  insured  by  the  arrangement  of  the  vessels  in  the  pia  mater,  in 
which,  previous  to  their  distribution  to  the  substance  of  the  brain,  the 
large  arteries  break  up  and  divide  into  innumerable  minute  branches 
ending  in  capillaries,  which,  after  frequent  communications  with  one 
another,  enter  the  brain,  and  carry  into  nearly  every  part  of  it  uniform 
and  equable  streams  of  blood.  The  arteries  are  also  enveloped  in  a  special 
lymphatic  sheath.  The  arrangement  of  the  veins  within  the  cranium  is 
also  peculiar.  The  large  venous  trunks  or  sinuses  are  formed  so  as  to  be 
scarcely  capable  of  change  of  size;  and  composed,  as  they  are,  of  the 
tough  tissue  of  the  dura  mater,  and,  in  somo  instances,  bounded  on  one 
side  by  the  bony  cranium,  they  are  not  compressible  by  any  force  which 
the  fulness  of  the  arteries  might  exercise  through  the  substance  of  the 
brain;  nor  do  they  admit  of  distension  when  the  flow  of  venous  blood 
from  the  brain  is  obstructed. 

The  general  uniformity  in  the  supply  of  blood  to  the  brain,  which'is 
thus  secured,  is  well  adapted,  not  only  to  its  functions,  but  also  to  its  con- 
dition as  a  mass  of  nearly  incompressible  substance  placed  in  a  cavity 
with  unyielding  walls.  These  conditions  of  the  brain  and  skull  have 
appeared,  indeed,  to  some,  enough  to  justify  the  opinion  that  the  quan- 
tity of  blood  in  the  brain  must  be  at  all  times  the  same.  It  was  found 
that  in  animals  bled  to  death,  without  any  aperture  being-  made  in  the 
cranium,  the  brain  became  pale  and  anaemic  like  other  parts.  And  in 
death  from  strangling  or  drowning,  congestion  of  the  cerebral  vessels; 
while  in  death  by  prussic  acid,  the  quantity  of  blood  in  the  cavity  of  the 


168  HAND-BOOK    OF    PHYSIOLOGY. 

cranium  was  determined  by  the  position  in  which  the  animal  was  placed 
after  death,  the  cerebral  vessels  being  congested  when  the  animal  was  sus- 
pended with  its  head  downward,  and  comparatively  empty  when  the 
animal  was  kept  suspended  by  the  ears.  '  That,  it  was  concluded,  although 
the  total  volume  of  the  contents  of  the  cranium  is  probably  nearly  always 
the  same,  yet  the  quantity  of  blood  in  it  is  liable  to  variation,  its  increase 
or  diminution  being  accompanied  by  a  simultaneous  diminution  or  in- 
crease in  the  quantity  of  the  cerebro-spinal  fluid,  which,  by  readily 
admitting  of  being  removed  from  one  part  of  the  brain  and  spinal  cord  to 
another,  and  of  being  rapidly  absorbed,  and  as  readily  effused,  would 
serve  as  a  kind  of  supplemental  fluid  to  the  other  contents  of  the  cranium, 
to  keep  it  uniformly  filled  in  case  of  variations  in  their  quantity  (Bur- 
rows). And  there  can  be  no  doubt  that,  although  the  arrangements  of 
the  blood-vessels,  to  which  reference  has  been  made,  ensure  to  the  brain 
an  amount  of  blood  which  is  tolerably  uniform,  yet,  inasmuch  as  with 
every  beat  of  the  heart  and  every  act  of  respiration,  and  under  many 
other  circumstances,  the  quantity  of  blood  in  the  cavity  of  the  cranium 
is  constantly  varying,  it  is  plain  that,  were  there  not  provision  made  for 
the  possible  displacement  of  some  of  the  contents  of  the  unyielding  bony 
case  in  which  the  brain  is  contained,  there  would  be  often  alternations  of 
excessive  pressure  with  insufficient  supply  of  blood.  Hence  we  may  con- 
sider that  the  cerebro-spinal  fluid  in  the  interior  of  the  skull  not  only 
subserves  the  mechanical  functions  of  fat  in  other  parts  as  &  packing 
material,  but  by  the  readiness  with  which  it  can  be  displaced  into  the 
spinal  canal,  provides  the  means  whereby  undue  pressure  and  insufficient 
supply  of  blood  are  equally  prevented. 

Chemical  Composition  of  Cerebro-spinal  Fluid. — The  cerebro-spinal 
fluid  is  transparent,  colorless,  not  viscid,  with  a  saline  taste  and  alkaline 
reaction,  and  is  not  affected  by  heat  or  acids.  It  contains  981-984  parts 
water,  sodium  chloride,  traces  of  potassium  chloride,  of  sulphates,  car- 
bonates, alkaline  and  earthy  phosphates,  minute  traces  of  urea,  sugar, 
sodium  lactate,  fatty  matter,  cholesterin,  and  albumen  (Flint). 

2.  In  Erectile  Structures. — The  instances  of  greatest  variation  in  the 
quantity  of  blood  contained,  at  different  times,  in  the  same  organs,  are 
found  in  certain  structures  which,  under  ordinary  circumstances,  are  soft 
and  flaccid,  but,  at  certain  times,  receive  an  unusually  large  quantity  of 
blood,  become  distended  and  swollen  by  it,  and  pass  into  the  state  which 
has  been  termed  erection.  Such  structures  are  the  corpora  caver  no  sa  and 
corpus  spongiosum  of  the  penis  in  the  male,  and  the  clitoris  in  the  female; 
and,  to  a  less- degree,  the  nipple  of  the  mammary  gland  in  both  sexes. 
The  corpus  cavernosum  penis,  which  is  the  best  example  of  an  erectile 
structure,  has  an  external  fibrous  membrane  or  sheath;  and  from  the 
inner  surface  of  the  latter  are  prolonged  numerous  fine  lamellae  which 


CIRCULATION    OF    THE    BLOOD.  169 

divide  its  cavity  into  small  compartments  looking  like  cells  when  they 
are  inflated.  Within  these  is  situated  the  plexus  of  veins  upon  which 
the  peculiar  erectile  property  of  the  organ  mainly  depends.  It  consists 
of  short  veins  which  very  closely  interlace  and  anastomose  with  each  other 
in  all  directions,  and  admit  of  great  variation  of  size,  collapsing  in  the 
passive  state  of  the  organ,  but,  for  erection,  capable  of  an  amount  of  dila- 
tation which  exceeds  beyond  comparison  that  of  the  arteries  and  veins 
which  convey  the  blood  to  and  from  them.  The  strong  fibrous  tissue 
lying  in  the  intervals  of  the  venous  plexuses,  and  the  external  fibrous 
membrane  or  sheath  with  which  it  is  connected,  limit  the  distension  of 
the  vessels,  and,  during  the  state  of  erection,  give  to  the  penis  its  con- 
dition of  tension  and  firmness.  The  same  general  condition  of  vessels 
exists  in  the  corpus  spongiosum  urethra?,  but  around  the  urethra  the 
fibrous  tissue  is  much  weaker  than  around  the  body  of  the  penis,  and 
around  the  glans  there  is  none.  The  venous  blood  is  returned  from  the 
plexuses  by  comparatively  small  veins;  those  from  the  glans  and 
^the  fore  part  of  the  urethra  empty  themselves  into  the  dorsal  veins  of  the 
penis;  those  from  the  cavernosum  pass  into  deeper  veins  which  issue  from 
the  corpora  cavernosa  at  the  crura  penis;  and  those  from  the  rest  of  the 
urethra  and  bulb  pass  more  directly  into  the  plexus  of  the  veins  about  the 
prostate.  For  all  these  veins  one  condition  is  the  same;  namely,  that 
they  are  liable  to  the  pressure  of  muscles  when  they  leave  the  penis.  The 
muscles  chiefly  concerned  in  this  action  are  the  erector  penis  and  acceler- 
ator urinae.  Erection  results  from  the  distension  of  the  venous  plexuses 
with  blood.  The  principal  exciting  cause  in  the  erection  of  the  penis  is 
nervous  irritation,  originating  in  the  part  itself,  or  derived  from  the  brain 
and  spinal  cord.  The  nervous  influence  is  communicated  to  the  penis  by 
the  pudic  nerves,  which  ramify  in  its  vascular  tissue:  and  after  their 
division  in  the  horse,  the  penis  is  no  longer  capable  of  erection. 

This  influx  of  the  blood  is  the  first  condition  necessary  for  erection, 
and  through  it  alone  much  enlargement  and  turgescence  of  the  penis 
may  ensue.  But  the  erection  is  probably  not  complete,  nor  maintained 
for  any  time  except  when,  together  with  this  influx,  the  muscles  already 
mentioned  contract,  and  by  compressing  the  veins,  stop  the  efflux  of 
blood,  or  prevent  it  from  being  as  great  as  the  influx. 

It  appears  to  be  only  the  most  perfect  kind  of  erection  that  needs  the 
help  of  muscles  to  compress  the  veins;  and  none  such  can  materially  as- 
sist the  erection  of  the  nipples,  or  that  amount  of  turgescence,  just  falling 
short  of  erection,  of  which  the  spleen  and  many  other  parts  are  capable. 
For  such  turgescence  nothing  more  seems  necessary  than  a  large  plexiform 
arrangement  of  the  veins,  and  such  arteries  as  may  admit,  upon  occasion, 
augmented  quantities  of  blood. 

(3,  4,  5.)  The  circulation  in  the  Lungs,  Liver,  and  Kidneys  will  be 
described  under  those  heads. 


170  HAND-BOOK    OF    PHYSIOLOGY. 

Agents  concerned  in  the  circulation. — Before  quitting  this  sub- 
ject it  will  be  as  well  to  bring  together  in  a  tabular  form  the  various 
agencies  concerned  in  maintaining  the  circulation. 

1.  The  Systole  and  Diastole  of  the  Heart,  the  former  pumping  into 
the  aorta  and  so  into  the  arterial  system  a  certain  amount  of  blood,  and 
the  latter  to  some  extent  sucking  in  the  blood  from  the  veins. 

2.  The  elastic  and  muscular  coats  of  the  arteries,  which  serve  to  keep 
up  an  equable  and  continuous  stream. 

3.  The  so-called  vital  capillary  force. 

4.  The  pressure  of  the  muscles  on  veins  ivith  valves,  and  the  slight 
rhythmic  contraction  of  the  veins. 

5.  Aspiration  of  the  Thorax  during  inspiration,  by  means  of  which 
the  blood  is  drawn  from  the  large  veins  into  the  thorax  (to  be  treated  of 
in  next  Chapter). 

DlSCOYEKY   OF  THE   CIRCULATION. 

Up  to  nearly  the  close  of  the  sixteenth  century  it  was  generally  be-* 
lieved  that  the  blood  passed  from  one  ventricle  to  the  other  through  fora- 
mina in  the  "septum  ventriculorum."  These  foramina  are  of  course 
purely  imaginary,  but  no  one  ventured  to  dispute  their  existence  till  Ser- 
vetus  boldly  stated  that  he  could  not  succeed  in  finding  them.  He  fur- 
ther asserted  that  the  blood  passed  from  the  Right  to  the  Left  side  of  the 
heart  by  way  of  the  lungs,  and  also  advanced  the  hypothesis  that  it  is  thus 
"revivified,"  remarking  that  the  Pulmonary  Artery  is  too  large  to  serve 
merely  for  the  nutrition  of  the  lungs  (a  theory  then  generally  accepted). 

Realdus,  Columbo,  and  Caesalpinus  added  several  important  observa- 
tions. The  latter  showed  that  the  blood  is  slightly  cooled  by  passing 
through  the  lungs,  also  that  the  veins  swell  up  on  the  distal  side  of  a  liga- 
ture. The  existence  of  valves  in  the  veins  had  previously  been  discovered 
by  Fabricius  of  Aquapendente,  the  teacher  of  Harvey. 

The  honor  of  first  demonstrating  the  general  course  of  the  circulation 
belongs  by  right  to  Harvey,  who  made  his  grand  discovery  about  1618. 
He  was  the  first  to  establish  the  muscular  structure  of  the  heart,  which 
had  been  denied  by  many  of  his  predecessors;  and  by  careful  study  of  its 
action  both  in  the  body  and  when  excised,  ascertained  the  order  of  con- 
traction of  its  cavities.  He  did  not  content  himself  with  inferences  from 
the  anatomy  of  the  parts,  bat  employed  the  experimental  method  of 
injection,  and  made  an  extensive  and  accurate  series  of  observations  on 
the  circulation  in  cold-blooded  animals.  He  forced  water  through  the 
Pulmonary  Artery  till  it  trickled  out  through  the  Left  Ventricle,  the  tip 
of  which  had  been  cut  off.  Another  of  his  experiments  was  to  fill  the 
Right  side  of  the  heart  with  water,  tie  the  Pulmonary  Artery  and  the 
Venae  Cavae  and  then  squeeze  the  Right  ventricle:  not  a  drop  could  be 
forced  through  into  the  Left  ventricle,  and  thus  he  conclusively  disproved 
the  existence  of  foramina  in  the  septum  ventriculorum.  "I  have  suffi- 
ciently proved,"  says  he,  "that  by  the  beating  of  the  heart  the  blood 
passes  from  the  veins  into  the  arteries  through  the  ventricles,  and  is  dis- 
tributed over  the  whole  body." 

"In  the  warmer  animals,  such  as  man,  the  blood  passes  from  the  Right 


CIRCULATION    OF    THE    BLOOD.  171 

Ventricle  of  the  Heart  through  the  Pulmonary  Artery  into  the  Lungs, 
and  thence  through  the  Pulmonary  Veins  into  the  Left  Auricle,  thence 
into  the  Left  Ventricle." 

.    Proofs  of  the  Circulation  of  the  Blood. — The  following  are  the 
main  arguments  by  which  Harvey  established  the  fact  of  the  circulation: — 

1.  The  heart  in  half  an  hour  propels  more  blood  than  the  whole  mass 
of  blood  in  the  body. 

2.  The  great  force  and  jetting  manner  with  which  the  blood  spurts 
from  an  opened  artery,  such  as  the  carotid,  with  every  beat  of  the  heart. 

3.  If  true,  the  normal  course  of  the  circulation  explains  why  after 
death  the  arteries  are  commonly  found  empty  and  the  veins  full. 

4.  If  the  large  veins  near  the  heart  were  tied  in  a  fish  or  snake,  the 
heart  became  pale,  flaccid,  and  bloodless;  on  removing  the  ligature,  the 
blood  again  flowed  into  the  heart.     If  the  artery  were  tied,  the  heart  be- 
came distended;  the  distension  lasting  until  the  ligature  was  removed. 

5.  The  evidence  to  be  derived  from  a  ligature  round  a  limb.     If  it  be 
drawn  very  tight,  no  blood  can  enter  the  limb,  and  it  becomes  pale  and 
cold.     If  the  ligature  be  somewhat  relaxed,  blood  can  enter  but  cannot 
leave  the  limb;  hence  it  becomes  swollen  and  congested.     If  the  ligature 
be  removed,  the  limb  soon  regains  its  natural  appearance. 

6.  The  existence  of  valves  in  the  veins  which  only  permit  the  blood 
to  flow  toward  the  heart. 

7.  The  general  constitutional  disturbance  resulting  from  the  introduc- 
tion of  a  poison  at  a  single  point,  e.  g.,  snake  poison. 

To  these  may  now  be  added  many  further  proofs  which  have  accumu- 
lated since  the  time  of  Harvey,  e.  g. : — 

8.  Wounds  of  arteries  and  veins.     In  the  former  case  haemorrhage  may 
be  almost  stopped  by  pressure  between  the  heart  and  the  wound,  in  the 
latter  by  pressure  beyond  the  seat  of  injury. 

9.  The  direct  observation  of  the  passage  of    blood  corpuscles   from 
small  arteries  through  capillaries  into  veins  in  all  transparent  vascular 
parts,  as  the  mesentery,  tongue  or  web  of  the  frog,  the  tail  or  gills  of  a, 
tadpole,  etc. 

10.  The  results  of  injecting  certain  substances  into  the  blood. 
Further,  it  is  obvious  that  the  mere  fact  of  the  existence  of  a  hollow 

muscular  organ  (the  heart)  with  valves  so  arranged  as  to  permit  the  blood 
to  pass  only  in  one  direction,  of  itself  suggests  the  course  of  the  circula- 
tion. The  only  part  of  the  circulation  which  Harvey  could  not  follow 
is  that  through  the  capillaries,  for  the  simple  reason  that  he  had  no  lenses- 
sufficiently  powerful  to  enable  him  to  see  it.  Mafpighi  (1661)  and  Leeu- 
wenhoek  (1668)  demonstrated  it  in  the  tail  of  the  tadpole  and  lung  of  the 
frog. 


CHAPTEK  VI. 

RESPIRATION. 

THE  maintenance  of  animal  life  necessitates  the  continual  absorption 
of  oxygen  and  excretion  of  carbonic  acid;  the  blood  being,  in  all  animals 
which  possess  a  well  developed  blood-vascular  system,  the  medium  by 
which  these  gases  are  carried.  By  the  blood,  oxygen  is  absorbed  from 
without  and  conveyed  to  all  parts  of  the  organism,  and,  by  the  blood, 
carbonic  acid,  which  comes  from  within,  is  carried  to  those  parts  by 
which  it  may  escape  from  the  body.  The  two  processes, — absorption 
of  oxygen  and  excretion  of  carbonic  acid, — are  complementary,  and 
their  sum  is  termed  the  process  of  Respiration. 

In  all  Vertebrata,  and  in  a  large  number  of  Invertebrata,  certain  parts, 
either  lungs  or  gills,  are  specially  constructed  for  bringing  the  blood  into 
proximity  with  the  aerating  medium  (atmospheric  air,  or  water  contain- 
ing air  in  solution).  In  some  of  the  lower  Vertebrata  (frogs  and  other 
naked  Amphibia)  the  skin  is  important  as  a  respiratory  organ,  and  is 
capable  of  supplementing,  to  some  extent,  the  functions  of  the  proper 
breathing  apparatus;  but  in  all -the  higher  animals,  including  man,  the 
respiratory  capacity  of  the  skin  is  so  infinitesimal  that  it  may  be  practi- 
cally disregarded. 

Essentially,  a  lung  or  gill  is  constructed  of  a  fine  transparent  mem- 
brane, one  surface  of  which  is  exposed  to  the  air  or  water,  as  the  case  may 
be,  while,  on  the  other,  is  a  network  of  blood-vessels, — the  only  separation 
between  the  blood  and  aerating  medium  being  the  thin  wall  of  the  blood- 
vessels, and  the  fine  membrane  on  one  side  of  which  vessels  are  distributed. 
The  diiference  between  the  simplest  and  the  most  complicated  respiratory 
membrane  is  one  of  degree  only. 

The  various  complexity  of  the  respiratory  membrane,  and  the  kind  of 
aerating  medium,  are  not,  however,  the  only  conditions  which  cause  a 
diiference  in  the  respiratory  capacity  of  different  animals.  The  number 
and  size  of  the  red  blood-corpuscles,  the  mechanism  of  the  breathing  ap- 
paratus, the  presence  or  absence  of  a  pulmonary  heart,  physiologically 
distinct  from  the  systemic,  are,  all  of  them,  conditions  scarcely  second 
in  importance. 

In  the  heart  of  man  and  all  other  Mammalia,  the  right  side  from  which 
the  blood  is  propelled  into  and  through  the  lungs  may  be  termed  the 


RESPIRATION. 


173 


"pulmonary"  heart;  while  the  left  side  is  " :  systemic  "  in  function.  In 
many  of  the  lower  animals,  however,  no  such  distinction  can  be  drawn. 
Thus,  in  Fish  the  heart  propels  the  blood  to  the  respiratory  organ  (gills); 
l)ii t  there  is  no  contractile  sac  corresponding  to  the  left  side  of  the  heart, 
to  propel  the  blood  directly  into  the  systemic  vessels. 

It  may  be  well  to  state  here  that  the  lungs  are  only  the  medium  for 
the  exchange,  on  the  part  of  the  blood,  of  carbonic  acid  for  oxygen.  They 
are  not  the  seat,  in  any  special  manner,  of  those  combustion-processes 
of  which  the  production  of  carbonic  acid  is  the  final  result.  These  occur 
in  all  parts  of  the  body — more  in  one  part,  less  in  another:  chiefly  in  the 
substance  of  the  tissues,  but  in  part  in  the  capillary  blood-vessels  contained 
in  them. 

THE  RESPIRATORY  PASSAGES  AND  TISSUES. 

The  object  of  respiration  is  the  interchange  of  gases  in  the  lungs;  for 
this  purpose  it  is  necessary  that  the  atmospheric  air  shall  pass  into  them 


and  be  expelled  from  them.     The  lungs  are  contained  in  the  chest  or 
thorax,  which  is  a  closed  cavity  having  no  communication  with  the  out- 


174  HAND-BOOK    OF    PHYSIOLOGY. 

side,  except  by  means  of  the  respiratory  passages.  The  air  enters  these 
passages  through  the  nostrils  or  through  the  mouth,  thence  it  passes 
through  the  larynx  into  the  trachea  or  windpipe,  which  about  the  middle 
of  the  chest  divides  into  two  tubes,  bronchi,  one  to  each  (right  and  left) 
lung. 

The  Larynx  is  the  upper  part  of  the  passage  which  ieaas  exclusively 
"to  the  lung;  it  is  formed  by  the  thyroid,  cricoid,  and  arytenoid  cartilages 
(Fig.  145),  and  contains  the  vocal  cords,  by  the  vibration  of  which  the 
voice  is  chiefly  produced.  These  vocal  cords  are  ligamentous  bands  at- 
tached to  certain  cartilages  capable  of  movement  by  muscles.  By  their 
approximation  the  cords  can  entirely  close  the  entrance  into  the  larynx; 
lout  under  the  ordinary  conditions,  the  entrance  of  the  larynx  is  formed 
by  a  more  or  less  triangular  chink  between  them,  called  the  rima  glot- 
tidis.  Projecting  at  an  acute  angle  between  the  base  of  the  tongue  and 
the  larynx  to  which  it  is  attached,  is  a  leaf-shaped  cartilage,  with  its 
larger  extremity  free,  called  the  epiglottis  (Fig.  145,  e).  The  whole  of  the 
larynx  is  lined  by  mucous  membrane,  which,  however,  is  extremely  thin 
over  the  cords.  At  its  lower  extremity  the  larynx  joins  the  trachea.1 
With  the  exception  of  the  epiglottis  and  the  so-called  cornicula  laryngis, 
the  cartilages  of  the  larynx  are  of  the  hyaline  variety! 

Structure  of  Epiglottis. — The  supporting  cartilage  is  composed  of 
yellow  elastic  cartilage,  enclosed  in  a  fibrous  sheath  (perichondrium), 
and  covered  on  both  sides  with  mucous  membrane.  The  anterior  surface, 
which  looks  toward  the  base  of  the  tongue,  is  covered  with  mucous  mem- 
iDrane,  the  basis  of  which  is  fibrous  tissue,  elevated  toward  both  surfaces  in 
the  form  of  rudimentary  papillae,  and  covered  with  several  layers  of 
squamous  epithelium.  In  it  ramify  capillary  blood-vesse.ls,  and  in  its 
meshes  are  a  large  number  of  lymphatic  channels.  Under  the  mucous 
membrane,  in  the  less  dense  fibrous  tissue  of  which  it  is  composed,  are  a 
number  of  tubular  glands.  The  posterior  or  laryngeal  surface  of  the 
epiglottis  is  covered  by  a  mucous  membrane,  similar  in  structure  to  that 
on  the  other  surface,  but  that  the  epithelial  coat  is  thinner,  the  number 
of  strata  of  cells  being  less,  and  the  papillse  few  and  less  distinct.  The 
fibrous  tissue  which  constitutes  the  mucous  membrane  is  in  great  part  of 
the  adenoid  variety,  and  this  is  here  and  there  collected  into  distinct  masses 
or  follicles.  The  glands  of  the  posterior  surface  are  smaller  but  more 
numerous  than  those  on  the  other  surface.  In  many  places  the  glands 
which  are  situated  nearest  to  the  perichondrium  are  directly  continuous 
through  apertures  in  the  cartilage  with  those  on  the  other  side,  and  often 
the  ducts  of  the  glands  from  one  side  of  the  cartilage  pass  through  and 
open  on  the  mucous  surface  of  the  other  side.  Taste  goblets  have  been 

1  A  detailed  account  of  the  structure  and  function  of  the  Larynx  will  be  found  in 
Chapter  XVI. 


RESPIRATION. 


175 


found  in  the  epithelium  of  the  posterior  surface  of  the  epiglottis,  and  in 
several  other  situations  in  the  laryngeal  mucous  membrane. 

The  Trachea  and  Bronchial  Tubes. — The  trachea  or  wind-pipe 
extends  froni  the  cricoid  cartilage,  which  is  on  a  level  with  the  fifth  cervi- 


FIG.  145. 


FIG.  146. 


FIG.  145.— Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from 
before,  h,  the  great  cornu  of  the  hyoid  bone;  e,  epiglottis;  £,  superior,  and  f,  inferior  cornu  of  the 
thyroid  cartilage;  c,  middle  of  the  cricoid  cartilage:  fr,  the  trachea,  showing  sixteen  cartilaginous 
rings:  6,  the  right,  and  6'.  the  left  bronchus.  (Allen  Thomson.  1  x  J^. 

FIG.  146.— Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from  be- 
hind, /i,  great  cornu  of  the  hyoid  bone ;  t,  superior,  and  t\  the  inferior  cornu  of  the  thyroid  cartilage ; 
e,  the  epiglottis;  a,  points  to  the  back  of  both  the  arytenoid  cartilages  which  are  surmounted  by  the 
cornicula;  c,  the  middle  ridge  on  the  back  of  the  cricoid  cartilage :  tr,  the  posterior  membranous  part 
of  the  trachea;  6,  6',  right  and  left  bronchi.  (Allen  Thomson.)  J& 

cal  vertebra,  to  a  point  opposite  the  third  dorsal  vertebra,  where  it  divides 
into  the  two  bronchi,  one  for  each  lung  (Fig.  146).  It  measures,  on  an 
average,  four  or  four-and-a-half  inches  in  length,  and  from  three-quarters 
of  an  inch  to  an  inch  in  diameter. 


176 


HAND-BOOK    OF    PHYSIOLOGY. 


Structure. — The  trachea  is  essentially  a  tube  of  fibro-elastic  membrane, 
within  the  layers  of  which  are  enclosed  a  series  of  cartilaginous  rings,  from 
sixteen  to  twenty  in  number.  These  rings  extend  only  around  the  front 
and  sides  of  the  trachea  (about  two-thirds  of  its  circumference),  and  are 
deficient  behind;  the  interval  between  their  posterior  extremities  being 
bridged  over  by  a  continuation  of  the  fibrous  membrane  in  which  they 
are  enclosed  (Fig.  145).  The  cartilages  of  the  trachea  and  bronchial 
tubes  are  of  the  hyaline  variety. 


FIG.  147.— Section  of  trachea,  a,  columnar  ciliated  epithelium;  6  and  c,  proper  structure  of  the 
mucous  membrane,  containing  elastic  fibres  cut  across  transversely;  d,  submucous  tissue  containing 
mucous  glands,  e,  separated  from  the  hyaline  cartilage,  g,  by  a  fine  fibrous  tissue,  /;  /i,  external  in- 
vestment of  fine  fibrous  tissue.  (S.  K.  Alcock.) 

Immediately  within  this  tube,  at  the  back,  is  a  layer  of  unstriped 
muscular  fibres,  which  extends,  transversely.,  between  the  ends  of  the  car- 
tilaginous rings  to  which  they  are  attached,  and  opposite  the  intervals 
between  them,  also;  their  evident  function  being  to  diminish,  when  re- 
quired, the  calibre  of  the  trachea  by  approximating  the  ends  of  the  car- 
tilages. Outside  these  are  a  few  longitudinal  bundles  of  muscular  tissue 
which,  like  the  preceding,  are  attached  both  to  the  fibrous  and  cartilagi- 
nous framework. 


RESPIRATION.  177 

The  mucous  membrane  consists  of  adenoid  tissue,  separated  from  the 
stratified  columnar  epithelium  which  lines  it  by  a  homogeneous  basement 
membrane.  This  is  penetrated  here  and  there  by  channels  which  connect 
the  adenoid  tissue  of  the  mucosa  with  the  intercellular  substance  of  the 
epithelium.  The  stratified  columnar  epithelium  is  formed  of  several 
layers  of  cells  (Fig.  147),  of  which  the  most  superficial  layer  is  ciliated, 
and  is  often  branched  downward  to  join  connective-tissue  corpuscles; 
while  between  these  branched  cells  are  smaller  elongated  cells  prolonged 
up  toward  the  surface  and  down  to  the  basement  membrane.  Beneath 
these  are  one  or  more  layers  of  more  irregularly  shaped  cells.  In  the 
deeper  part  of  the  mucosa  are  many  elastic  fibres  between  which  lie  con- 
nective-tissue corpuscles  and  capillary  blood-vessels. 

Numerous  mucous  glands  are  situate  on  the  exterior  and  in  the 
substance  of  the  fibrous  framework  of  the  trachea;  their  ducts  perfora- 
ting the  various  structures  which  form  the  wall  of  the  trachea,  and. 
opening  through  the  mucous  membrane  into  the  interior. 

The  two  bronchi  into  which  the  trachea  divides,  of  which  the  right  is 
shorter,  broader,  and  more  horizontal  than  the  left  (Fig.  145),  resemble 
the  trachea  exactly  in  structure,  and  in  the  arrangement  of  their  carti- 
laginous rings.  On  entering  the  substance  of  the  lungs,  however,  the; 
rings,  although  they  still  form  only  larger  or  smaller  segments  of  a  circle,, 
are  no  longer  confined  to  the  front  and  sides  of  the  tubes,  but  are  dis- 
tributed impartially  to  all  parts  of  their  circumference. 

The  bronchi  divide  and  subdivide,  in  the  substance  of  the  lungs,  into 
a  number  of  smaller  and  smaller  branches,  which  penetrate  into  every 
part  of  the  organ,  until  at  length  they  end  in  the  smaller  subdivisions 
of  the  lungs,  called  lobules. 

All  the  larger  branches  still  have  walls  formed  of  tough  membrane, 
containing  portions  of  cartilaginous  rings,  by  which  they  are  held  open, 
and  unstriped  muscular  fibres,  as  well  as  longitudinal  bundles  of  elastic 
tissue.  They  are  lined  by  mucous  membrane,  the  surface  of  which,  like 
that  of  the  larynx  and  trachea,  is  covered  with  ciliated  epithelium  (Fig. 
148).  The  mucous  membrane  is  abundantly  provided  with  mucous 
glands. 

As  the  bronchi  become  smaller  and  smaller,  and  their  walls  thinner, 
the  cartilaginous  rings  become  scarcer  and  more  irregular,  until,  in  the 
smaller  bronchial  tubes,  they  are  represented  only  by  minute  and  scattered 
cartilaginous  flakes.  And  when  the  bronchi,  by  successive  branches,  are 
reduced  to  about  ^  of  an  inch  in  diameter,  they  lose  their  cartilaginous 
element  altogether,  and  their  walls  are  formed  only  of  a  tough  fibrous 
elastic  membrane,  with  circular  muscular  fibres;  they  are  still  lined,  how- 
ever, by  a  thin  mucous  membrane,  with  ciliated  epithelium,  the  length  of 
the  cells  bearing  the  cilia  having  become  so  far  diminished,  that  the  cells 
are  now  almost  cubical.  In  the  smaller  bronchi  the  circular  muscular 
VOL.  I.— 12. 


178 


HAND-BOOK    OF    PHYSIOLOGY 


fibres  are  more  abundant  than  in  the  trachea  and  larger  bronchi,  and  form 
a  distinct  circular  coat. 

The  Lungs  and  Pleura. — The  Lungs  occupy  the  greater  portion  of 
the  thorax.  They  are  of  a  spongy  elastic  texture,  and  on  section  appear 
to  the  naked  eye  as  if  they  were  in  great  part  solid  organs,  except  here 
and  there,  at  certain  points,  where  branches  of  the  bronchi  or  air-tubes 
may  have  been  cut  across,  and  show,  on  the  surface  of  the  section,  their 


FIG.  148.— Transverse  section  of  a  bronchus,  about  one-fourth  of  an  inch  in  diameter,  e,  Epithe- 
lium (ciliated);  immediately  beneath  it  is  the  mucous  membrane  or  internal  fibrous  layer,  of  varying 
thickness;  m,  muscular  layer;  s,  m,  submucous  tissue;  /,  fibrous  tissue;  c,  cartilage  enclosed  within 
the  layers  of  fibrous  tissue;  gr,  mucous  gland.  (F.  E.  Schulze.) 

tubular  structure.  In  fact,  however,  the  lungs  are  hollow  organs,  each 
of  which  communicates  by  a  separate  orifice  with  a  common  air-tube,  the 
trachea. 

The  Pleura. — Each  lung  is  enveloped  by  a  serous  membrane — the 
pleura,  one  layer  of  which  adheres  closely  to  the  surface  of  the  lung, 


FIG.  149.— Transverse  section  of  the  chest  (after  Gray). 

and  provides  it  with  its  smooth  and  slippery  covering,  while  the  other 
adheres  to  the  inner  surface  of  the  chest- wall.  The  continuity  of  the 
two  layers,  which  form  a  closed  sac,  as  in  the  case  of  other  serous  mem- 
branes, will  be  best  understood  by  reference  to  Fig.  149.  The  appearance 


KESPIRATION.  179 

of  a  space,  however,  between  the  pleura  which  covers  the  lung  (visceral 
layer),  and  that  which  lines  the  inner  surf  ace  of  the  chest  (jwrttfoi  layer), 
is  inserted  in  the  drawing  only  for  the  sake  of  distinctness.  These  layers 
are,  in  health,  everywhere  in  contact,  one  with  the  other;  and  between 
them  is  only  just  so  much  fluid  as  will  ensure  the  lungs  gliding  easily,  in 
their  expansion  and  contraction,  on  the  inner  surface  of  the  parietal 
layer,  which  lines  the  chest-wall.  While  considering  the  subject  of 
normal  respiration,  we  may  discard  altogether  the  notion  of  the  existence 
of  any  space  or  cavity  between  the  lungs  and  the  wall  of  the  chest. 

If,  however,  an  opening  be  made  so  as  to  permit  air  or  fluid  to  enter 
the  pleural  sac,  the  lung,  in  virtue  of  its  elasticity,  recoils,  and  a  consid- 
erable space  is  left  between  the  lung  and  the  chest- wall.  In  other  words, 
the  natural  elasticity  of  the  lungs  would  cause  them  at  all  times  to  con- 
tract away  from  the  ribs,  were  it  not  that  the  contraction  is  resisted  by 
atmospheric  pressure  which  bears  only  on  the  inner  surface  of  the  air- 
tubes  and  air-cells.  On  the  admission  of  air  into  the  pleural  sac,  atmos- 
pheric pressure  bears  alike  on  the  inner  and  outer  surfaces  of  the  lung, 
and  their  elastic  recoil  is  thus  no  longer  prevented. 

Structure  of  the  Pleura  and  Lung. — The  pulmonary  pleura  consists 
of  an  outer  or  denser  layer  and  an  inner  looser  tissue.  The  former  or 
pleura  proper  consists  of  dense  fibrous  tissue  with  elastic  fibres,  covered 
by  endothelium,  the  cells  of  which  are  large,  flat,  hyaline,  and  transpar- 
ent when  the  lung  is  expanded,  but  become  smaller,  thicker,  and  gran- 
ular when  the  lung  collapses.  In  the  pleura  is  a  lymph-canalicular 
system;  and  connective  tissue  corpuscles  are  found  in  the  fibres  and  tissue 
which  forms  its  groundworr.  The  inner,  looser,  or  subpleural  tissue 
contains  lamellae  of  fibrous  connective  tissue  and  connective  tissue  cor- 
puscles between  them.  Numerous  lymphatics  are  to  be  met  with,  which 
form  a  dense  plexus  of  vessels,  many  of  which  contain  valves.  They  are 
simple  endothelial  tubes,  and  take  origin  in  the  lymph-canalicular  system 
of  the  pleura  proper.  Scattered  bundles  of  unstriped  muscular  fibre 
occur  in  the  pulmonary  pleura.  They  are  especially  strongly  developed 
on  those  parts  (anterior  and  internal  surfaces  of  lungs)  which  move  most 
freely  in  respiration:  their  function  is  doubtless  to  aid  in  expiration.  The 
structure  of  the  parietal  portion  of  the  pleura  is  very  similar  to  that  of 
the  visceral  layer. 

Each  lung  is  partially  subdivided  into  separate  portions  called  lobes; 
the  right  lung  into  three  lobes,  and  the  left  into  two.  Each  of  these 
lobes,  again,  is  composed  of  a  large  number  of  minute  parts,  called  lobules. 
Each  pulmonary  lobule  may  be  considered  a  lung  in  miniature,  consist- 
ing, ^as  it  does,  of  a  branch  of  the  bronchial  tube,  of  air-cells,  blood 
vessels,  nerves,  and  lymphatics,  with  a  sparing  amount  of  areolar 
tissue. 

On  entering  a  lobule,  the  small  bronchial  tube,  the  structure  of  which 


180 


HAND-BOOK    OF    PHYSIOLOGY. 


has  been  just  described  (a,  Fig.  150),  divides  and  subdivides;  its  walls 
at  the  same  time  becoming  thinner  and  thinner,  until  at  length  they  are 
formed  only  of  a  thin  membrane  of  areolar  and  elastic  tissue,  lined  by  a 
layer  of  squamous  epithelium,  not  provided  with  cilia.  At  the  same 
time,  they  are  altered  in  shape;  each  of  the  minute  terminal  branches 


FIG.  150.— Ciliary  epithelium  of  the  human  trachea,  a,  Layer  of  longitudinally  arranged  elastic 
fibres;  6,  basement  membrane;  c,  deepest  cells,  circular  in  form;  d,  intermediate  elongated  cells;  ey 
outermost  layer  of  cells  fully  developed  and  bearing  cilia.  X  350.  (Kolliker.) 

i 

widening  out  funnel-wise,  and  its  walls  being  pouched  out  irregularly 
into  small  saccular  dilatations,  called  air-cells  (Fig.  151,  Z>).  Such  a 
funnel-shaped  terminal  branch  of  the  bronchial  tube,  with  its  group  of 
pouches  or  air-cells,  has  been  called  an  infundibulum  (Figs.  151,  152), 


FIG.  151.  FIG.  152. 

FIG.  151.— Terminal  branch  of  a  bronchial  tube,  with  its  infundibula  and  air-cells,  from  tte  mar- 
gin of  the  lung  of  a  monkey,  injected  with  quicksilver,  a,  terminal  bronchial  twig;  6  6,  infundibula 
and  air-cells,  X  10.  (F.  E.  Shulze.) 

FIG.  152.— Two  small  infundibula  or  groups  of  air-cells,  a  a,  with  air-cells,  6  6,  and  the  ultimate 
bronchial  tubes,  c  c,  with  which  the  air-cells  communicate.  From  a  new-born  child.  (Kolliker.) 

and  the  irregular  oblong  space  in  its  centre,  with  which  the  air-cells  com- 
municate, an  intercellular  passage. 

The  air-cells,  or  air- vesicles,  may  be  placed  singly,  like  recesses  from, 
the  intercellular  passage,  but  more  often  they  are  arranged  in  groups  or 


RESPIRATION. 


181 


even  in  rows,  like  minute  sacculated  tubes;  so  that  a  short  series  of 
vesicles,  all  communicating  with  one  another,  open  by  a  common  orifice 
into  the  tube.  The  vesicles  are  of  various  forms,  according  to  the  mutual 
pressure  to  which  they  are  subject;  their  walls  are  nearly  in  contact,  and 
thcv  vary  from  -^  to  ^  of  an  inch  in  diameter.  Their  walls  are  formed 
of  fine  membrane,  similar  to  that  of  the  intercellular  passages,  and  con- 
tinuous with  it,  which  membrane  is  folded  on  itself  so  as  to  form  a  sharp- 
edged  border  at  each  circular  orifice  of  communication  between  con- 
tiguous air-vesicles,  or  between  the  vesicles  and  the  bronchial  passages. 
Numerous  fibres  of  elastic  tissue  are  spread  out  between  contiguous  air- 


Fio.  153. — From  a  section  of  lung  of  a  cat,  stained  with  silver  nitrate.  A.  D.  Alveolar  duct  or  in- 
tercellular passage.  S.  Alveolar  septa.  N.  Alveoli  or  air-cells,  lined  with  large  flat,  nucleated  cells, 
with  some  smaller  polyhedral  nucleated  cells.  Circular  muscular  fibres  are  seen  surrounding  the  in- 
terior of  the  alveolar  duct,  and  at  one  part  is  seen  a  group  of  small  polyhedral  cells  continued  from 
the  bronchus.  (Klein  and  Noble  Smith.) 

cells,  and  many  of  these  are  attached  to  the  outer  surface  of  the  fine 
membrane  of  which  each  cell  is  composed,  imparting  to  it  additional 
strength,  and  the  power  of  recoil  after  distension.  The  cells  are  lined  by 
a  layer  of  epithelium  (Fig.  153),  not  provided  with  cilia.  Outside  the 
cells,  a  network  of  pulmonary  capillaries  is  spread  out  so  densely  (Fig. 
154),  that  the  interspaces  or  meshes  are  even  narrower  than  the  vessels, 
which  are,  on  an  average,  -g-gVff  °^  an  inch  in  diameter.  Between  the 
atmospheric  air  in  the  cells  and  the  blood  in  these  vessels,  nothing  inter- 
venes but  the  thin  walls  of  the  cells  and  capillaries;  and  the  exposure  of 
the  blood  to  the  air  is  the  more  complete,  because  the  folds  of  membrane 
between  contiguous  cells,  and  often  the  spaces  between  the  walls  of  the 


182  HAND-BOOK    OF    PHYSIOLOGY. 

same,  contain  only  a  single  layer  of  capillaries,  both  sides  of  which  are 
thus  at  once  exposed  to  the  air. 

The  air-vesicles  situated  nearest  to  the  centre  of  the  lung  are  smaller 
and  their  networks  of  capillaries  are  closer  than  those  nearer  to  the  cir- 
cumference. The  vesicles  of  adjacent  lobules  do  not  communicate;  and 
those  of  the  same  lobule  or  proceeding  from  the  same  intercellular  passage, 
do  so  as  a  general  rule  only  near  angles  of  bifurcation;  so  that,  when 
any  bronchial  tube  is  closed  or  obstructed,  the  supply  of  air  is  lost  for  all 
the  cells  opening  into  it  or  its  branches. 

Blood-supply. — The  lungs  receive  blood  from  two  sources,  (a)  the  pul- 
monary artery,  (b)  the  bronchial  arteries.  The  former  conveys  venous 
blood  to  the  lungs  for  its  arterialization,  and  this  blood  takes  no  share  in 
the  nutrition  of  the  pulmonary  tissues  through  which  it  passes.  (#)  The 


FIG.  154.— Capillary  network  of  the  pulmonary  blood- vessels  in  the  human  lung.  x60.  (Kolliker.) 

branches  of  the  bronchial  arteries  ramify  for  nutrition's  sake  in  the  walls 
of  the  bronchi,  of  the  larger  pulmonary  vessels,  in  the  interlobular  con- 
nective tissue,  etc.;  the  blood  of  the  bronchial  vessels  being  returned 
chiefly  through  the  bronchial  and  partly  through  the  pulmonary  veins. 

Lymphatics. — The  lymphatics  are  arranged  in  three  sets: — 1.  Irreg- 
ular lacunae  in  the  walls  of  the  alveoli  or  air-cells.  The  lymphatic  vessels 
which  lead  from  these  accompany  the  pulmonary  vessels  toward  the  root 
of  the  lung.  2.  Irregular  anastomosing  spaces  in  the  walls  of  the 
bronchi.  3.  Lymph-spaces  in  the  pulmonary  pleura.  The  lymphatic 
vessels  from  all  these  irregular  sinuses  pass  in  toward  the  root  of  the  lung 
to  reach  the  bronchial  glands. 

Nerves. — The  nerves  of  the  lung  are  to  be  traced  from  the  anterior 
and  posterior  pulmonary  plexuses,  which  are  formed  by  branches  of  the 
vagus  and  sympathetic.  The  nerves  follow  the  course  of  the  vessels  and 
bronchi,  and  in  the  walls  of  the  latter  many  small  ganglia  are  situated. 


RESPIRATION.  183 


MECHANISM  OF  RESPIRATION. 

Respiration  consists  of  the  alternate  expansion  and  contraction  of  the 
thorax,  by  means  of  which  air  is  drawn  into  or  expelled  from  the  lungs. 
These  acts  are  called  Inspiration  and  Expiration  respectively. 

For  the  inspiration  of  air  into  the  lungs  it  is  evident  that  all  that  is 
necessary  is  such  a  movement  of  the  side- walls  or  floor  of  the  chest,  or  of 
both,  that  the  capacity  of  the  interior  shall  be  enlarged.  By  such  in- 
crease of  capacity  there  will  be  of  course  a  diminution  of  the  pressure  of 
the  air  in  the  lungs,  and  a  fresh  quantity  will  enter  through  the  larynx  and 
trachea  to  equalize  the  pressure  on  the  inside  and  outside  of  the  chest. 

For  the  expiration  of  air,  on  the  other  hand,  it  is  also  evident  that, 
by  an  opposite  movement  which  shall  diminish  the  capacity  of  the  chest, 
the  pressure  in  the  interior  will  be  increased,  and  air  will  be  expelled, 
until  the  pressures  within  and  without  the  chest  are  again  equal.  In  both 
cases  the  air  passes  through  the  trachea  and  larynx,  whether  in  entering 
or  leaving  the  lungs,  there  being  no  other  communication  with  the  exterior 
of  the  body;  and  the  lung,  for  the  same  reason,  remains  under  all  the 
circumstances  described  closely  in  contact  with  the  walls  and  floor  of  the 
chest.  To  speak  of  expansion  of  the  chest,  is  to  speak  also  of  expansion 
of  the  lung. 

AVe  have  now  to  consider  the  means  by  which  the  respiratory  move- 
ments are  effected. 


RESPIRATORY  MOVEMENTS. 

A.  Inspiration. — The  enlargement  of  the  chest  in  inspiration  is  a 
muscular  act;  the  effect  of  the  action  of  the  inspiratory  muscles  being  an 
increase  in  the  size  of  the  chest-cavity  (a)  in  the  vertical,  and  (b)  in  the 
lateral  and  antero-posterior  diameters.  The  muscles  engaged  in  ordinary 
inspiration  are  the  diaphragm;  the  external  intercostals;  parts  of  the  in- 
ternal intercostals;  the  levatores  costarum;  and  serratus  posticus  superior. 

(a. )  The  vertical  diameter  of  the  chest  is  increased  by  the  contraction 
and  consequent  descent  of  the  diaphragm, — the  sides  of  the  muscle  de- 
scending most,  and  the  central  tendon  remaining  comparatively  unmoved; 
while  the  intercostal  and  other  muscles,  by  acting  at  the  same  time,  pre- 
vent the  diaphragm,  during  its  contraction,  from  drawing  in  the  sides 
of  the  chest. 

(b. )  The  increase  in  the  lateral  and  antero-posterior  diameters  of  the 
chest  is  effected  by  the  raising  of  the  ribs,  the  greater  number  of  which 
are  attached  very  obliquely  to  the  spine  and  sternum  (see  Figure  of  Skele- 
ton in  frontispiece). 

The  elevation  of  the  ribs  takes  place  both  in  front  and  at  the  sides — 


184 


HAND-BOOK    OF    PHYSIOLOGY. 


the  hinder  ends  being  prevented  from  performing  any  upward  movement 
by  their  attachment  to  the  spine.  The  movement  of  the  front  extremities 
of  the  ribs  is  of  necessity  accompanied  by  an  upward  and  forward  move- 
ment of  the  sternum  to  which  they  are  attached,  the  movement  being 
greater  at  the  lower  end  than  at  the  upper  end  of  the  latter  bone. 


FIG.  155. — Diagram  of  axes  of  movement  of  ribs. 


The  axes  of  rotation  in  these  movements  are  two;  one  corresponding 
with  a  line  drawn  through  the  two  articulations  which  the  rib  forms  with 
the  spine  (a  b,  Fig.  155);  and  the  other,  with  a  line  drawn  from  one  of 
these  (head  of  rib)  to  the  sternum  (A  B,  Fig.  155,  and  Fig.  156);  the 


FIG.  156.— Diagram  of  movement  of  a  rib  in  inspiration. 

motion  of  the  rib  around  the  latter  axis  being  somewhat  after  the  fashion 
of  raising  the  handle  of  a  bucket. 

The  elevation  of  the  ribs  is  accompanied  by  a  slight  opening  out  of  the 


RESPIRATION. 


1*5 


angle  whicli  the  bony  part  forms  with  its  cartilage  (Fig.  156,  A);  and 
thus  an  additional  means  is  provided  for  increasing  the  antero-posterior 
diameter  of  the  chest. 

The  muscles  by  which  the  ribs  are  raised,  in  ordinary  quiet  inspiration, 
are  the  external  inter costals,  and  that  portion  of  the  internal  intercostal* 
which  is  situate  between  the  costal  cartilages;  and  these  are  assisted  by 
the  levatores  costarum,  and  the  serratus  posticus  superior.  The  action 
of  the  levatores  and  the  serratus  is  very  simple.  Their  fibres,  arising 
from  the  spine  as  a  fixed  point,  pass  obliquely  downward  and  forward  to 
the  ribs,  and  necessarily  raise  the  latter  when  they  contract.  The  action 
of  the  intercostal  muscles  is  not  quite  so  simple,  inasmuch  as,  passing 
merely  from  rib  to  rib,  they  seem  at  first  sight  to  have  no  fixed  point 
toward  which  they  can  pull  the  bones  to  which  they  are  attached. 

A  very  simple  apparatus  will  explain  this  apparent  anomaly  and  make 
their  action  plain.  Such  an  apparatus  is  shown  in  Fig.  157.  A  B  is  an 
upright  bar,  representing  the  spine,  with  which  are  jointed  two  parallel 
bars,  C  and  D,  which  represent  two  of  the  ribs,  and  are  connected  in 
front  by  movable  joints  with  another  upright,  representing  the  sternum. 


> 


FIG.  157. 


FIG.  158. 


FIG.  157.— Diagram  of  apparatus  showing  the  action  of  the  external  intercostal  muscles. 
FIG.  158.— Diagram  of  apparatus  showing  the  action  of  the  internal  intercostal  muscles. 


If  with  such  an  apparatus  elastic  bands  be  connected  in  imitation  of 
the  intercostal  muscles,  it  will  be  found  that  when  stretched  011  the  bars 
after  the  fashion  of  the  external  intercostal  fibres  (Fig.  157,  C  D),  i.e., 
passing  downward  and  forward,  they  raise  them  (Fig.  157,  C'  D');  while 
on  the  other  hand,  if  placed  in  imitation  of  the  position  of  the  internal 
intercostals  (Fig.  158,  E  F),  i.e.,  passing  downward  and  backward,  they 
depress  them  (Fig.  158,  E'  F'). 

,  The  explanation  of  the  foregoing  facts  is  very  simple.    The  intercostal 
muscles,  in  contracting,  merely  do  that  which  all  other  contracting  fibres 


186  HAND-BOOK    OF    PHYSIOLOGY. 

do,  viz.,  bring  nearer  together  the  points  to  which  they  are  attached; 
and  in  order  to  do  this,  the  external  intercostals  must  raise  the  ribs,  the 
points  C  and  D  (Fig.  157)  being  nearer  to  each  other  when  the  parallel 
bars  are  in  the  position  of  the  dotted  lines.  The  limit  of  the  movement 
in  the  apparatus  is  reached  when  the  elastic  band  extends  at  right  angles 
to  the  two  bars  which  it  connects — the  points  oi;  attachment  C'  and  D' 
being  then  at  the  smallest  possible  distance  one  from  the  other. 

The  internal  intercostals  (excepting  those  fibres  which  are  attached 
to  the  cartilages  of  the  ribs),  have  an  opposite  action  to  that  of  the  exter- 
nal. In  contracting  they  must  pull  down  the  ribs,  because  the  points  E 
and  F  (Fig.  158)  can  only  be  brought  nearer  one  to  another  (Fig.  158, 
E'  F')  by  such  an  alteration  in  their  position. 

On  account  of  the  oblique  position  of  the  cartilages  of  the  ribs  with 
reference  to  the  sternum,  the  action  of  the  inter-cartilaginous  fibres  of 
the  internal  intercostals  must,  of  course,  on  the  foregoing  principles,  re- 
semble that  of  the  external  intercostals. 

In  tranquil  breathing,  the  expansive  movements  of  the  lower  part  of 
the  chest  are  greater  than  those  of  the  upper.  In  forced  inspiration,  on 
the  other  hand,  the  greatest  extent  of  movement  appears  to  be  in  the 
upper  antero-posterior  diameter. 

Muscles  of  Extraordinary  Inspiration. — In  extraordinary  or 
forced  inspiration,  as  in  violent  exercise,  or  in  cases  in  which  there  is 
some  interference  with  the  due  entrance  of  air  into  the  chest,  and  in 
which,  therefore,  strong  efforts  are  necessary,  other  muscles  than  those 
just  enumerated,  are  pressed  into  the  service.  It  is  very  difficult  or  im- 
possible to  separate  by  a  hard  and  fast  line,  the  so-called  muscles  of  ordi- 
nary from  those  of  extraordinary  inspiration;  but  there  is  no  doubt  that 
the  following  are  but  little  used  as  respiratory  agents,  except  in  cases  in 
which  unusual  efforts  are  required — the  scaleni  muscles,  the  sternomas- 
toid,  the  serratus  magnus,  the  pectorales,  and  the  trapezius. 

Types  of  Respiration. — The  expansion  of  the  chest  in  inspiration 
presents  some  peculiarities  in  different  persons.  In  young  children,  it  is 
effected  chiefly  by  the  diaphragm,  which  being  highly  arched  in  expiration, 
becomes  flatter  as  it  contracts,  and,  descending,  presses  on  the  abdominal 
viscera,  and  pushes  forward  the  front  walls  of  the  abdomen.  The  move- 
ment of  the  abdominal  walls  being  here  more  manifest  than  that  of  any 
other  part,  it  is  usual  to  call  this  the  abdominal  type  of  respiration.  In 
men,  together  with  the  descent  of  the  diaphragm,  and  the  pushing  for- 
ward of  the  front  wall  of  the  abdomen,  the  chest  and  the  sternum  are 
subject  to  a  wide  movement  in  inspiration  (inferior  costal  type).  In 
women,  the  movement  appears  less  extensive  in  the  lower,  and  more  so 
in  the  upper,  part  of  the  chest  (superior  costal  type).  (See  Figs.  159, 
160.) 

B.  Expiration. — From  the  enlargement  produced  in  inspiration, 
the  chest  and  lungs  return  in  ordinary  tranquil  expiration,  by  their  elas- 
ticity; the  force  employed  by  the  inspiratory  muscles  in  distending  the 


RESPIRATION. 


187 


chest  and  overcoming  the  elastic  resistance  of  the  lungs  and  chest-walls, 
being  returned  as  an  expiratory  effort  when  the  muscles  are  relaxed. 
This  elastic  recoil  of  the  lungs  is  sufficient,  in  ordinary  quiet  breathing, 
to  expel  air  from  the  chest  in  the  intervals  of  inspiration,  and  no  muscular 
power  is  required.  In  all  voluntary  expiratory  efforts,  however,  as  in  speak- 
ing, singing,  blowing,  and  the  like,  and  in  many  involuntary  actions  also, 
as  sneezing,  coughing,  etc.,  something  more  than  merely  passive  elastic 
power  is  necessary,  and  the  proper  expiratory  muscles  are  brought  into 
action.  By  far  the  chief  of  these  are  the  abdominal  muscles,  which,  by 


FIG.  159. 


FIG.  160. 


FIG.  159.— The  changes  of  the  thoracic  and  abdominal  walls  of  the  male  during  respiration.  The 
back  is  supposed  to  be  fixed,  in  order  to  throw  forward  the  respiratory  movement  as  much  as  possi- 
ble. The  outer  black  continuous  line  in  front  represents  the  ordinary  breathing  movement:  the  ante- 
rior margin  of  it  being  the  boundary  of  inspiration,  the  posterior  margin  the  limit  of  expiration.  The 
line  is  thicker  over  the  abdomen,  since  the  ordinary  respiratory  movement  is  chiefly  abdominal ;  thin 
over  the  chest,  for  there  is  less  movement  over  that  region.  The  dotted  line  indicates  the  movement 
on  deep  inspiration,  during  which  the  sternum  advances  while  the  abdomen  recedes. 

FIG.  160. — The  respiratory  movement  in  the  female.  The  lines  indicate  the  same  changes  as  in 
the  last  figure.  The  thickness  of  the  continuous  line  over  the  sternum  shows  the  larger  extent  of  the 
ordinary  breathing  movement  over  that  region  in  the  female  than  in  the  male.  (John  Hutcninson.) 

The  posterior  continuous  line  represents  in  both  figures  the  limit  of  forced  expiration. 


pressing  on  the  viscera  of  the  abdomen,  push  up  the  floor  of  the  chest 
formed  by  the  diaphragm,  and  by  thus  making  pressure  on  the  lungs, 
expel  air  from  them  through  the  trachea  and  larynx.  All  muscles,  how- 
ever, which  depress  the  ribs,  must  act  also  as  muscles  of  expiration,  and 
therefore  we  must  conclude  that  the  abdominal  muscles  are  assisted  in 
their  action  by  the  greater  part  of  the  internal  intercostals,  the  triangu- 
laris  sterni,  the  serratus  posticus  inferior,  and  quadratus  lumborum. 
When  by  the  efforts  of  the  expiratory  muscles,  the  chest  has  been  squeezed 
to  less  than  its  average  diameter,  it  again,  on  relaxation  of  the  muscles, 
returns  to  the  normal  dimensions  by  virtue  of  its  elasticity.  The  con- 


188  HAND-BOOK    OF    PHYSIOLOGY. 

struction  of  the  chest-walls,  therefore,  admirably  adapts  them  for  recoiling 
against  and  resisting  as  well  undue  contraction  as  undue  dilatation. 

In  the  natural  condition  of  the  parts,  the  lungs  can  never  contract  to 
the  utmost,  but  are  always  more  or  less  "on  the  stretch/'  being  kept 
closely  in  contact  with  the  inner  surface  of  the  walls  of  the  chest  by 
atmospheric  pressure,  and  can  contract  away  from  these  only  when,  by 
some  means  or  other,  as  by  making  an  opening  into  the  pleural  cavity,  or 
by  the  effusion  of  fluid  there,  the  pressure  on  the  exterior  and  interior  of 
the  lungs  becomes  equal.  Thus,  under  ordinary  circumstances,  the 
degree  of  contraction  or  dilatation  of  the  lungs  is  dependent  on  that  of 
the  boundary  walls  of  the  chest,  the  outer  surface  of  the  one  being  in 
close  contact  with  the  inner  surface  of  the  other,  and  obliged  to  follow  it 
in  all  its  movements. 

Respiratory  Rhythm. — The  acts  of  expansion  and  contraction  of 
the  chest,  take  up,  under  ordinary  circumstances,  a  nearly  equal  time. 
The  act  of  inspiring  air,  however,  especially  in  women  and  children,  is  a 
little  shorter  than  that  of  expelling  it,  and  there  is  commonly  a  very 
slight  pause  between  the  end  of  expiration  and  the  beginning  of  the  next 
inspiration.  The  respiratory  rhythm  may  be  thus  expressed: — 

Inspiration 6 

Expiration 7  or  8 

A  very  slight  pause. 

Respiratory  Sounds. — If  the  ear  be  placed  in  contact  with  the  wall 
of  the  chest,  or  be  separated  from  it  only  by  a  good  conductor  of  sound, 
a  faint  respiratory  murmur  is  heard  during  inspiration.  This  sound 
varies  somewhat  in  different  parts — being  loudest  or  coarsest  in  the  neigh- 
borhood of  the  trachea  and  large  bronchi  (tracheal  and  bronchial  breath- 
ing), and  fading  off  into  a  faint  sighing  as  the  ear  is  placed  at  a  distance 
from  these  (vesicular  breathing).  It  is  best  heard  in  children,  and  in 
them  a  faint  murmur  is  heard  in  expiration  also.  The  cause  of  the  vesic- 
ular murmur  has  received  various  explanations.  Most  observers  hold 
that  the  sound  is  produced  by  the  friction  of  the  air  against  the  walls  of 
the  alveoli  of  the  lungs  when  they  are  undergoing  distension  (Laennec, 
Skoda),  others  that  it  is  due  to  an  oscillation  of  the  current  of  air  as  it 
enters  the  alveoli  (Chauveau),  whilst  others  believe  that  the  sound  is  pro- 
duced in  the  glottis,  but  that  it  is  modified  in  its  passage  to  the  pulmo- 
nary alveoli  (Beau,  Gee). 

Respiratory  Movements  of  the  Nostrils  and  of  the  Glottis.— 
During  the  action  of  the  muscles  which  directly  draw  air  into  the  chest, 
those  which  guard  the  opening  through  which  it  enters  are  not  passive. 
In  hurried  breathing  the  instinctive  dilatation  of  the  nostrils  is  well  seen, 
although  under  ordinary  conditions  it  may  not  be  noticeable.  The  open- 
ing at  the  upper  part  of  the  larynx,  however,  or  rima  glottidis  (Fig.  297), 


RESPIRATION.  189 

is  dilated  at  each  inspiration,  for  the  more  ready  passage  of  air,  and  be- 
comes smaller  at  each  expiration;  its  condition,  therefore,  corresponding 
during  respiration  with  that  of  the  walls  of  the  chest.  There  is  a  further 
likeness  between  the  two  acts  in  that,  under  ordinary  circumstances,  the 
dilatation  of  the  rima  glottidis  is  a  muscular  act,  and  itc  contraction 
chiefly  an  elastic  recoil;  although,  under  various  conditions,  to  be  here- 
after mentioned,  there  may  be,  in  the  contraction  of  the  glottis,  consider- 
able muscular  power  exercised. 

Terms  used  to  express  Quantity  of  Air  breathed. — Breathing 
or  tidal  air,  is  the  quantity  of  air  which  is  habitually  and  almost  uni- 
formly changed  in  each  act  of  breathing.  In  a  healthy  adult  man  it  is 
about  30  cubic  inches. 

Complemented  air,  is  the  quantity  over  and  above  this  which  can  be 
drawn  into  the  lungs  in  the  deepest  inspiration;  its  amount  is  various,  as 
will  be  presently  shown. 

Reserve  air.  After  ordinary  expiration,  such  as  that  which  expels  the 
breathing  or  tidal  air,  a  certain  quantity  of  air  remains  in  the  lungs, 
which  may  be  expelled  by  a  forcible  and  deeper  expiration.  This  is 
termed  reserve  air. 

Residual  air  is  the  quantity  which  still  remains  in  the  lungs  after  the 
most  violent  expiratory  effort.  Its  amount  depends  in  great  measure  on 
the  absolute  size  of  the  chest,  but  may  be  estimated  at  about  100  cubic 
inches. 

The  total  quantity  of  air  which  passes  into  and  out  of  the  lungs  of  an 
adult,  at  rest,  in  24  hours,  is  about  686,000  cubic  inches.  This  quantity, 
however,  is  largely  increased  by  exertion;  the  average  amount  for  a  hard- 
working laborer  in  the  same  time,  being  1,568,390  cubic  inches. 

Respiratory  Capacity. — The  greatest  respiratory  capacity  of  the  chest 
is  indicated  by  the  quantity  of  air  which  a  person  can  expel  from  his  lungs 
by  a  forcible  expiration  after  the  deepest  inspiration  that  he  can  make; 
it  expresses  the  power  which  a  person  has  of  breathing  in  the  emergencies 
of  active  exercise,  violence,  and  disease.  The  average  capacity  of  an 
adult  (at  60°  F.  or  15 '4°  C.)  is  about  225  cubic  inches. 

The  respiratory  capacity,  or  as  Hutchinson  called  it,  vital  capacity, 
is  usually  measured  by  a  modified  gasometer  (spirometer  of  Hutchinson), 
into  which  the  experimenter  breathes, — making  the  most  prolonged  ex- 
piration possible  after  the  deepest  possible  inspiration.  The  quantity  of 
air  which  is  thus  expelled  from  the  lungs  is  indicated  by  the  height  to 
which  the  air  chamber  of  the  spirometer  rises;  and  by  means  of  a  scale 
placed  in  connection  with  this,  the  number  of  cubic  inches  is  read  off. 

In  healthy  men,  the  respiratory  capacity  varies  chiefly  with  the  stature, 
weight,  and  age. 

It  was  found  by  Hutchinson,  from  whom  most  of  our  information  on 


190  HAND-BOOK    OF    PHYSIOLOGY. 

this  subject  is  derived,  that  at  a  temperature  of  60°  F.,  225  cubic  inches 
is  the  average  vital  or  respiratory  capacity  of  a  healthy  person,  five  feet 
seven  inches  in  height 

Circumstances  affecting  the  amount  of  respiratory  capacity. — For 
every  inch  of  height  above  this  standard  the  capacity  is"  increased,  on  an 
average,  by  eight  cubic  inches;  and  for  every  inch  below,  it  is  diminished 
by  the  same  amount. 

The  influence  of  weight  on  the  capacity  of  respiration  is  less  manifest 
and  considerable  than  that  of  height;  and  it  is  difficult  to  arrive  at  any 
definite  conclusions  on  this  point,  because  the  natural  average  weight  of 
a  healthy  man  in  relation  to  stature  has  not  yet  been  determined.  As  a 
general  statement,  however,  it  may  be  said  that  the  capacity  of  respiration 
is  not  affected  by  weights  under  161  pounds,  or  11|-  stones;  but  that, 
above  this  point,  it  is  diminished  at  the  rate  of  one  cubic  inch  for  every 
additional  pound  up  to  196  pounds,  or  14  stones. 

By  age,  the  capacity  appears  to  be  increased  from  about  the  fifteenth 
to  the  thirty-fifth  year,  at  the  rate  of  five  cubic  inches  per  year;  from 
thirty-five  to  sixty-five  it  diminishes  at  the  rate  of  about  one  and  a  half 
cubic  inch  per  year;  so  that  the  capacity  of  respiration  of  a  man  of  sixty 
years  old  would  be  about  30  cubic  inches  less  than  that  of  a  man  forty 
years  old,  of  the  same  height  and  weight.  (John  Hutchinson.) 

Number  of  Respirations,  and  Relation  to  the   Pulse. — The 

number  of  respirations  in  a  healthy  adult  person  usually  ranges  from 
fourteen  to  eighteen  per  minute.  It  is  greater  in  infancy  and  childhood. 
It  varies  also  much  according  to  different  circumstances,. such  as  exercise 
or  rest,  health,  or  disease,  etc.  Variations  in  the  number  of  respirations 
correspond  ordinarily  with  similar  variations  in  the  pulsations  of  the 
heart.  In  health  the  proportion  is  about  1  to  4,  or  1  to  5,  and  when  the 
rapidity  of  the  heart's  action  is  increased,  that  of  the  chest  movement 
is  commonly  increased  also;  but  not  in  every  case  in  equal  proportion. 
It  happens  occasionally  in  disease,  especially  of  the  lungs  or  air-passages, 

Vthat  the  number  of  respiratory  acts  increases  in  quicker  proportion  than 
the  beats  of  the  pulse;  and,  in  other  affections,  much  more  commonly, 
that  the  number  of  the  pulses  is  greater  in  proportion  than  that  of  the 
respirations. 

There  can  be  no  doubt  that  the  number  of  respirations  of  any  given 
animal  is  largely  affected  by  its  size.  Thus,  comparing  animals  of  the 
same  kind,  in  a  tiger  (lying  quietly)  the  number  of  respirations  was  20  per 
minute,  while  in  a  small  leopard  (lying  quietly)  the  number  was  30.  In 
a  small  monkey  40  per  minute;  in  a  large  baboon,  20. 

The  rapid,  panting  respiration  of  mice,  even  when  quite  still,  is 
familiar,  and  contrasts  strongly  with  the  slow  breathing  of  a  large  animal 
such  as  the  elephant  (eight  or  nine  times  per  minute).  These  facts  may 
be  explained  as  follows: — The  heat-producing  power  of  any  given  animal 
depends  largely  on  its  bulk,  while  its  loss  of  heat  depends  to  a  great 
extent  upon  the  surface  area  of  its  body.  If  of  two  animals  of  similar 
shape,  one  be  ten  times  as  long  as  the  other,  the  area  of  the  large  animal 


RESPIRATION.  I  9 1 

(representing  its  loss  of  heat)  is  100  times  that  of  the  small  one,  while  its 
bulk  (representing  production  of  heat)  is  about  1000  times  as  great. 
Thus  in  order  to  balance  its  much  greater  relative  loss  of  heat,  the  smaller 
animal  must  vhave  all  its  vital  functions,  circulation,  respiration,  etc., 
carried  on  much  more  rapidly. 

Force  of  Inspiratory  and  Expiratory  Muscles.— The  force  with 
which  the  inspiratory  muscles  are  capable  of  acting  is  greatest  in  individ- 
uals of  the  height  of  from  five  feet  seven  inches  to  five  feet  eight  inches,, 
and  will  elevate  a  column  of  three  inches  of  mercury.  Above  this  height, 
the  force  decreases  as  the  stature  increases;  so  that  the  average  of  men 
of  six  feet  can  elevate  only  about  two  and  a  half  inches  of  mercury.  The 
force  manifested  in  the  strongest  expiratory  acts  is,  on  the  average,  one- 
third  greater  than  that  exercised  in  inspiration.  But  this  difference  is 
in  u'reat  measure  due  to  the  power  exerted  by  the  elastic  reaction  of  the 
walls  of  the  chest;  and  it  is  also  much  influenced  by  the  disproportionate 
strength  which  the  expiratory  muscles  attain,  from  their  being  called  into 
use  for  other  purposes  than  that  of  simple  expiration.  The  force  of  the 
inspiratory  act  is,  therefore,  better  adapted  than  that  of  the  expiratory  for 
testing  the  muscular  strength  of  the  body.  (John  Hutchinson.) 

The  instrument  used  by  Hutchinson  to  gauge  the  inspiratory  and  ex- 
piratory power  was  a  mercurial  manometer,  to  which  was  attached  a  tube 
fitting  the  nostrils,  and  through  which  the  inspiratory  or  expiratory 
effort  was  made.  The  following  table  represents  the  results  of  numerous 
experiments: 

Power  of  Power  of 

Inspiratory  Muscles.  Expiratory  Muscles. 

1-5  in.  Weak  2'0  in. 


2-0 


3-5 
4-5 
5-5 

6-0 

7-0 


Ordinary          .  .     2'5 

Strong     .         .  .     3'5 

Very  strong     .  .4*5 

Kemarkable      .  .     5'8 

Very  remarkable  .     7*0 

Extraordinary  .     8  '5 

Very  extraordinary  .   10 '0 


. . 


The  greater  part  of  the  force  exerted  in  deep  inspiration  is  employed 
in  overcoming  the  resistance  offered  by  the  elasticity  of  the  walls  of  the 
•chest  and  of  the  lungs. 

The  amount  of  this  elastic  resistance  was  estimated  by  observing  the 
elevation  of  a  column  of  mercury  raised  by  the  return  of  air  forced,  after 
death,  into  the  lungs,  in  quantity  equal  to  the  known  capacity  of  respira- 
tion during  life;  and  Hutchinson  calculated,  according  to  the  well-known 
hydrostatic  law  of  equality  of  pressures  (as  shown  in  the  Bramah  press), 
that  the  total  force  to  be  overcome  by  the  muscles  in  the  act  of  inspiring 
;200  cubic  inches  of  air  is  more  than  450  Ibs. 


192  HAND-BOOK    OF    PHYSIOLOGY. 

The  elastic  force  overcome  in  ordinary  inspiration  is,  according  to  the 
same  authority,  equal  to  about  170  Ibs. 

Douglas  Powell  has  shown  that  within  the  limits  of  ordinary  tranquil 
respiration,  the  elastic  resilience  of  the  walls  of  the  chest  favors  inspira- 
tion; and  that  it  is  only  in  deep  inspiration  that  the  ribs  and  rib-cartilages 
offer  an  opposing  force  to  their  dilatation.  In  other  words,  the  elastic 
resilience  of  the  lungs,  at  the  end  of  an  act  of  ordinary  breathing,  has 
drawn  the  chest -walls  within  the  limits  of  their  normal  degree  of  expan- 
sion. Under  all  circumstances,  of  course,  the  elastic  tissue  of  the  lungs 
opposes  inspiration,  and  favors  expiration. 

Functions  of  Muscular  Tissue  of  Lungs.— It  is  possible  that  the 
contractile  power  which  the  bronchial  tubes  and  air-vesicles  possess,  by 
means  of  their  muscular  fibres  may  (1)  assist  in  expiration;  but  it  is  more 
likely  that  its  chief  purpose  is  (2)  to  regulate  and  adapt,  in  some  measure, 
the  quantity  of  air  admitted  to  the  lungs,  and  to  each  part  of  them, 
according  to  the  supply  of  blood;  (3)  the  muscular  tissue  contracts  upon 
and  gradually  expels  collections  of  mucus,  which  may  have  accumulated 
within  the  tubes,  and  cannot  be  ejected  by  forced  expiratory  efforts,  owing 
to  collapse  or  other  morbid  conditions  of  the  portion  of  lung  connected 
with  the  obstructed  tubes  (Gairdner).  (4)  Apart  from  any  of  the  before- 
mentioned  functions,  the  presence  of  muscular  fibre  in  the  walls  of  a  hol- 
low viscus,  such  as  a  lung,  is  only  what  might  be  expected  from  analogy 
with  o.ther  organs.  Subject  as  the  lungs  are  to  such  great  variation  in 
size  it  might  be  anticipated  that  the  elastic  tissue,  which  enters  so  largely 
into  their  composition,  would  be  supplemented  by  the  presence  of  much 
muscular  fibre  also. 

EESPIRATOEY  CHANGES  IK  THE  Am  AKD  IK  THE  BLOOD. 

A.  In  the  Air. 

Composition  of  the  Atmosphere. — The  atmosphere  we  breathe  has,  in 
every  situation  in  which  it  has  been  examined  in  it*  natural  state,  a  nearly 
uniform  composition.  It  is  a  mixture  of  oxygen,  nitrogen,  carbonic 
acid,  and  watery  vapor,  with,  commonly,  traces  of  other  gases,  as  ammonia, 
sulphuretted  hydrogen,  etc.  Of  every  100  volumes  of  pure  atmospheric 
air,  79  volumes  (on  an  average)  consist  of  nitrogen,  the  remaining  21  of 
oxygen.  By  weight  the  proportion  is  N.  75,  0.  25.  The  proportion  of 
carbonic  acid  is  extremely  small;  10,000  volumes  of  atmospheric  air  con- 
tain only  about  4  or  5  of  carbonic  acid. 

The  quantity  of  watery  vapor  varies  greatly  according  to  the  temper- 
ature and  other  circumstances,  but  the  atmosphere  is  never  without  some. 
In  this  country,  the  average  quantity  of  watery  vapor  in  the  atmosphere 
is  1  '40  per  cent. 


RESPIRATION.  193 

Composition  of  Air  which  has  been  breathed. — The  changes  effected  by 
respiration  in  the  atmospheric  air  are:  1,  an  increase  of  temperature;  2, 
an  increase  in  the  quantity  of  carbonic  acid;  3,  a  diminution  in  the  quan- 
tity of  oyxgen;  4,  a  diminution  of  volume;  5,  an  increase  in  the  amount 
of  watery  vapor;  6,  the  addition  of  a  minute  amount  of  organic  matter 
and  of  free  ammonia. 

1.  The  expired  air,  heated  by  its  contact  with  the  interior  of  the 
lungs,   is  (at  least  in  most  climates)  hotter  than  the  inspired  air.     Its 
temperature  varies  between  97°  and  99.5°  F.  (36° — 37 '5°  C.),  the  lower 
temperature  being  observed  when  the  air  has  remained  but  a  short  time 
in  the  lungs.     Whatever  may  be  the  temperature  of  the  air  when  inhaled, 
it  nearly  acquires  that  of  the  blood  before  it  is  expelled  from  the  chest. 

2.  The  Carbonic  Acid  in  respired  air  is  always  increased;  but  the 
quantity  exhaled  in  a  given  time  is  subject  to  change  from  various  cir- 
cumstances.    From  every  volume  of  air  inspired,  about  4 '8  per  cent,  of 
oxygen  is  abstracted;  while  a  rather  smaller  quantity,  4*3,  of  carbonic 
acid  is  added  in  its  place:  the  air  will  contain,  therefore,  434  vols.  of  car- 
bonic acid  in  10,000.     Under  ordinary  circumstances,  the  quantity  of 
carbonic  acid  exhaled  into  the  air  breathed  by  a  healthy  adult  man  amounts 
to  1346  cubic  inches,  or  about  636  grains  per  hour.     According  to  this  esti- 
mate, the  weight  of  carbon  excreted  from  the  lungs  is  about  173  grains 
per  hour,  or  rather  more  than  8  ounces  in  twenty-four  hours.     These 
quantities  must  be  considered  approximate  only,  inasmuch  as  various  cir- 
cumstances, even  in  health,  influence  the  amount  of  carbonic  acid  ex- 
creted, and,  correlatively,  the  amount  of  oxygen  absorbed. 

Circumstances  influencing  the  amount  of  carbonic  acid  excreted. — The 
following  are  the  chief: — Age  and  sex.  'Eespiratory  movements.  Ex- 
ternal temperature.  Season  of  year.  Condition  of  respired  air.  Atmos- 
pheric conditions.  Period  of  the  day.  Food  and  drink.  Exercise  and 
sleep. 

a.  Age  and  Sex. — The  quantity  of  carbonic  acid  exhaled  into  the  air 
breathed  by  males,  regularly  increases  from  eight  to  thirty  years  of  age; 
from  thirty  to  fifty  the  quantity,  after  remaining  stationary  for  awhile, 
gradually  diminishes,  and  from  fifty  to  extreme  age  it  goes  on   diminish- 
ing, till  it  scarcely  exceeds  the  quantity  exhaled  at  ten  years  old.     In 
females  (in  whom  the  quantity  exhaled  is  always  less  than  in  males  of  the 
same  age)  the  same  regular  increase  in  quantity  goes  on  from  the  eighth 
year  to  the  age  of  puberty,  when  the  quantity  abruptly  ceases  to  increase, 
and  remains  stationary  so  long  as  they  continue  to  menstruate.     When 
menstruation  has  ceased,  it  soon  decreases  at  the  same  rate  as  it  does  in 
old  men. 

b.  Respiratory  Movements. — The  more  quickly  the  movements  of 
respiration  are  performed,  the  smaller  is  the  proportionate  quantity  of 
carbonic  acid  contained  in  each  volume  of  the  expired  air.     Although, 
however,  the  proportionate  quantity  of  carbonic  acid  is  thus  diminished 
during  frequent  respiration,  yet  the  absolute  amount  exhaled  into  the  air 
within  a  given  time  is  increased  thereby,  owing  to  the  larger  quantity  of 

VOL.  I.— 13. 


194  HAND-BOOK    OF   PHYSIOLOGY. 

air  which  is  breathed  in  the  time.  The  last  half  of  a  volume  of  expired 
air  contains  more  carbonic  acid  than  the  half  first  expired;  a  circumstance 
•which  is  explained  by  the  one  portion  of  air  coming  from  the  remote  part 
of  the  lungs,  where  it  has  been  in  more  immediate  and  prolonged  contact 
with  the  blood  than  the  other  has,  which  comes  chiefly  from  the  larger 
bronchial  tubes. 

c.  External  temperature. — The  observation  made  by  Vierordt  at  vari^ 
ous  temperatures  between  38°  F.  and  75° T.  (3'4°— 23 '8°  C.)  show,  for 
warm-blooded  animals,  that  within  this  range,  every  rise  equal  to  10°  F. 
causes  a  diminution  of  about  two  cubic  inches  in  the  quantity  of  carbonic 
acid  exhaled  per  minute. 

d.  Season  of  the   Year. — The  season  of  the  year,  independently  of 
temperature,  materially  influences  the  respiratory  phenomena;  spring  being 
the  season  of  the  greatest,  and  autumn  of  the  least  activity  of  the  res- 
piratory and  other  functions.     (Edward  Smith.) 

e.  Purity  of  the  Respired  Air. — The  average  quantity  of  carbonic  acid 
given  out  by  the  lungs  constitutes  about  4*3  per  cent,  of  the  expired 
air;  but  if  the  air  which  is  breathed  be  previously  impregnated  with  car- 
bonic acid  (as  is  the  case  when  the  same  air  is  frequently  respired),  then 
the  quantity  of  carbonic  acid  exhaled  becomes  much  less. 

/.  Hygrometric  State  of  Atmosphere. — The  amount  of  carbonic  acid 
exhaled  is  considerably  influenced  by  the  degree  of  moisture  of  the  atmos- 
phere, much  more  being  given  off  when  the  air  is  moist  than  when  it  is 
dry.  (Lehmann.) 

g.  Period  of  the  Day. — During  the  daytime  more  carbonic  acid  is  ex- 
haled than  corresponds  to  the  oxygen  absorbed;  while,  on  the  other  hand, 
at  night  very  much  more  oxygen  is  absorbed  than  is  exhaled  in  carbonic 
acid.  There  is,  thus,  a  reserve  fund  of  oxygen  absorbed  by  night  to  meet 
the  requirements  of  the  day.  If  the  total  quantity  of  carbonic  acid  ex- 
haled in  24  hours  be  represented  by  100,  52  parts  are  exhaled  during  the 
day,  and  48  at  night.  While,  similarly,  33  parts  of  the  oxygen  are  ab- 
sorbed during  the  day,  and  the  remaining  67  by  night.  (Pettenkofer  and 
Voit.) 

h.  Food  and  Drink. — By  the  use  of  food  the  quantity  is  increased, 
whilst  by  fasting  it  is  diminished;  it  is  greater  when  animals  are  fed  on 
farinaceous  food  than  when  fed  on  meat.  The  effects  produced  by  spiritu- 
ous drinks  depend  much  on  the  kind  of  drink  taken.  Pure  alcohol  tends 
rather  to  increase  than  to  lessen  respiratory  changes,  and  the  amount 
therefore  of  carbonic  acid  expired;  rum,  ale,  and  porter,  also  sherry,  have 
very  similar  effects.  On  the  other  hand,  brandy,  whisky,  and  gin,  par- 
ticularly the  latter,  almost  always  lessened  the  respiratory  changes,  and 
consequently  the  amount  of  carbonic' acid  exhaled.  (Edward  Smith.) 

i.  Exercise — Bodily  exercise,  in  moderation,  increases  the  quantity 
to  about  one-third  more  than  it  is  during  rest:  and  for  about  an  hour 
after  exercise  the  volume  of  the  air  expired  in  the  minute  is  increased 
about  118  cubic  inches:  and  the  quantity  of  carbonic  acid  about  7*8  cubic 
inches  per  minute.  Violent  exercise,  such  as  full  labor  on  the  tread  wheel, 
still  further  increases  the  amount  of  the  acid  exhaled.  (Edward  Smith.) 

A  larger  quantity  is  exhaled  when  the  barometer  is  low  than  when  it 
is  high. 

3.  The  oxygen  is  diminished,  and  its  diminution  is  generally  propor- 
tionate to  the  increase  of  the  carbonic  acid. 


RESPIRATION.  195 

For  every  volume  of  carbonic  acid  exhaled  into  the  air,  1  -17421  volumes 
of  oxygen  are  absorbed  from  it,  and  1346  cubic  inches,  or  636  grains,  be- 
ing exhaled  in  the  hour,  the  quantity  of  oxygen  absorbed  in  the  same  tirrte 
is  1584  cubic  inches,  or  542  grains.  According  to  this  estimate,  there  is 
more  oxygen  absorbed  than  is  exhaled  with  carbon  to  form  carbonic  acid. 

4.  The  volume  of  air  expired  in  a  given  time  is  less  than  that  of  the 
air  inspired  (allowance  being  made  for  the  expansion  in  being  heated), 
niul  that  the  loss  is  due  to  a  portion  of  oxygen  absorbed  and  not  returned 
in  the  exhaled  carbonic  acid,  all  observers  agree,  though  as  to  the  actual 
quantity  of  oxygen  so  absorbed,  they  differ  even  widely.     The  amount  of 
oxygen  absorbed  is  on  an  average  4 -8  per  cent.,  so  that  the  expired  air 
contains  l(j'2  volumes  per  cent,  of  that  gas. 

The  quantity  of  oxygen  that  does  not  combine  with  the  carbon  given 
off  in  carbonic  acid  from  the  lungs  is  probably  disposed  of  in  forming 
some  of  the  carbonic  acid  and  water  given  off  from  the  skin,  and  in  com- 
bining with  sulphur  and  phosphorus  to  form  part  of  the  acids  of  the  sul- 
phates and  phosphates  excreted  in  the  urine,  and  probably  also,  with  the 
nitrogen  of  the  decomposing  nitrogenous  tissues.  (Bence  Jones.) 

The  quantity  of  oxygen  in  the  atmosphere  surrounding  animals,  ap- 
pears to  have  very  little  influence  on  the  amount  of  this  gas  absorbed  by 
them,  for  the  quantity  consumed  is  not  greater  even  though  an  excess  of 
oxygen  be  added  to  the  atmosphere  experimented  with. 

It  has  often  been  discussed  whether  Nitrogen  is  absorbed  by  or  exhaled 
from  the  lungs  during  respiration.  At  present,  all  that  can  be  said  on 
the  subject  is  that,  under  most  circumstances,  animals  appear  to  expire 
a  very  small  quantity  above  that  which  exhts  in  the  inspired  air.  During 
prolonged  fasting,  on  the  contrary,  a  small  quantity  appears  to  be  ab- 
sorbed. 

5.  The  watery  vapor  is  increased.     The  quantity  emitted  is,  as  a  gen- 
eral rule,  sufficient  to  saturate  the  expired  air,  or  very  nearly  so.    Its  abso- 
lute amount  is,  therefore,  influenced  by  the  following  circumstances,  (1), 
by  the  quantity  of  air  respired;  for  the  greater  this  is,  the  greater  also 
will  be  the  quantity  of  moisture  exhaled.     (2),  by  the  quantity  of  watery 
vapor  contained  in  the  air  previous  to  its  being  inspired;    because  the 
greater  this  is,  the  less  will  be  the  amount  required  to  complete  the  satu- 
ration of  the  air;    (3),  by  the  temperature  of  the  expired  air;  for  the 
higher  this  is,  the  greater  will  be  the  quantity  of  watery  vapor  required 
to  saturate  the  air;  (4),  by  the  length  of  time  which  each  volume  of  in- 
spired air  is  allowed  to  remain  in  the  lungs;  for  although,  during  ordinary 
respiration,  the  expired  air  is  always  saturated  with  watery  vapor,  yet 
when  respiration  is  performed  very  rapidly  the  air  has  scarcely  time  to  be 
raised  to  the  highest  temperature,  or  be  fully  charged  with  moisture  ere 
it  is  expelled. 


196  HAND-BOOK    OF    PHYSIOLOGY. 

.  t  The  quantity  of  water  exhaled  from  the  lungs  in  twenty-four  hours 
ranges  (according  to  the  various  modifying  circumstances  already  men- 
tioned) from  about  6  to  27  ounces,  the  ordinary  quantity  being  about  9 
or  10  ounces.  Some  of  this  is  probably  formed  by  the  chemical  combina- 
tion of  oxygen  with  hydrogen  in  the  system;  but  the  far  larger  propor- 
tion of  it  is  water  which  has  been  absorbed,  as  such,  into  the  blood  from 
the  alimentary  canal,  and  which  is  exhaled  from  the  surface  of  the  air- 
passages  and  cells,  as  it  is  from  the  free  surfaces  of  all  moist  animal  mem- 
branes, particularly  at  the  high  temperature  of  warm-blooded  animals. 

6.  A  small  quantity  of  ammonia  is  added  to  the  ordinary  constituents 
of  expired  air.     It  seems  probable,  however,  both  from  the  fact  that  this 
substance  cannot  be  always  detected,  and  from  its  minute  amount  when 
present,  that  the  whole  of  it  may  be  derived  from  decomposing  particles 
of  food  left  in  the  mouth,  or  from  carious  teeth  or  the  like;  and  that  it 
is,  therefore,  only  an  accidental  constituent  of  expired  air. 

7.  The  quantity  of  organic  matter  in  the  breath  is  about  3  grains  in 
twenty-four  hours.     (Ransome.) 

The  following  represents  the  kind  of  experiment  by  which  the  fore- 
going facts  regarding  the  excretion  of  carbonic  acid,  water,  and  organic 
matter,  have  been  established. 

A  bird  or  mouse  is  placed  in  a  large  bottle,  through  the  stopper  of 
which  two  tubes  pass,  one  to  supply  fresh  air,  and  the  other  to  carry  off 
that  which  has  been  expired.  Before  entering  the  bottle,  the  air  is 
made  to  bubble  through  a  strong  solution  of  caustic  potash,  which  absorbs 
the  carbonic  acid,  and  then  through  lime-water,  which  by  remaining 
limpid,  proves  the  absence  of  carbonic  acid.  The  air  which  has  been 
breathed  by  the  animal  is  made  to  bubble  through  lime  water,  which  at 
once  becomes  turbid  and  soon  quite  milky  from  the  precipitation  of  cal- 
cium carbonate;  and  it  finally  passes  through  strong  sulphuric  acid, 
which,  by  turning  brown,  indicates  the  presence  of  organic  matter.  The 
watery  vapor  in  the  expired  air  will  condense  inside  the  bottle  if  the  sur- 
face be  kept  cool. 

By  means  of  an  apparatus  sufficiently  large  and  well  constructed, 
exp  Briments  of  the  kind  have  been  made  extensively  on  man. 


METHODS  BY  WHICH  THE  KESPIRATORY  CHANGES  IN  THE  AIR  ARE 

EFFECTED. 

The  method  by  which  fresh  air  is  inhaled  and  expelled  from  the  lungs 
has  been  considered.  It  remains  to  consider  how  it  is  that  the  blood 
absorbs  oxygen  from,  and  gives  up  carbonic  acid  to,  the  air  of  the  alveoli. 
In  the  first  place,  it  must  be  remembered  that  the  tidal  air  only  amounts 
to  about  25. — 30  cubic  inches  at  each  inspiration,  and  that  this  is  of  course 
insufficient  to  fill  the  lungs,  but  it  mixes  with  the  stationary  air  by  diffu- 
sion, and  so  supplies  to  it  new  oxygen.  The  amount  of  oxygen  in  expired 
air,  which  may  be  taken  as  the  average  composition  of  the  mixed  air  in 


RESPIRATION.  197 

the  lungs,  is  about  16  to  17 per  cent.;  in  the  pulmonary  alveoli  it  may  be 
rather  less  than  this.  From  this  air  the  venous  blood  has  to  take  up  oxy- 
gen in  the  proportion  of  8  to  12  vols.  in  every  hundred  volumes  of  blood, 
as  the  difference  between  the  amount  of  oxygen,  in  arterial  and  venous 
blood  is  no  less  than  that.  It  seems  therefore  somewhat  difficult  to  un- 
derstand how  this  can  be  accomplished  at  the  low  oxygen  tension  of  the 
pulmonary  air.  But  as  was  pointed  out  in  a  previous  Chapter  (IV.),  the 
oxygen  is  not  simply  dissolved  in  the  blood,  but  is  to  a  great  extent 
chemically  combined  with  the  haemoglobin  of  the  red  corpuscles;  and  when 
a  fluid  contains  a  body  which  enters  into  loose  chemical  combination  in 
this  way  with  a  gas,  the  tension  of  the  gas  in  the  fluid  is  not  directly  pro- 
portional to  the  total  quantity  of  the  ga£  taken  up  by  the  fluid,  but  to  the 
excess  above  the  total  quantity  which  the  substance  dissolved  in  the  fluid 
is  capable  of  taking  up  (a  known  quantity  in  the  case  of  haemoglobin, 
viz.,  1-59  cm.  for  one  grm.  haemoglobin).  Ojt  the  other  hand,  if  the  sub- 
stance be  not  saturated,  i.e.,  if  it  be  not  combined  with  as  much  of  the 
gas  as  it  is  capable  of  taking  up,  further  combination  leads  to  no  increase 
of  its  tension.  However,  there  is  a  point  at  which  the  haemoglobin  gives 
up  its  oxygen  when  it  is  exposed  to  a  low  partial  pressure  of  oxygen,  and 
there  is  also  a  point  at  which  it  neither  takes  up  nor  gives  out  oxygen; 
in  the  case  of  arterial  blood  of  the  dog,  this  is  found  to  be  when  the  oxy- 
gen tension  of  the  atmosphere  is  equal  to  3*9  per  cent,  (or  29*6  mm.  of 
mercury),  which  is  equivalent  to  saying  that  the  oxygen  tension  of  arterial 
blood  is  3  -9  per  cent. ;  venous  blood,  in  a  similar  manner,  has  been  found 
to  have  an  oxygen  tension  of  2*8  per  cent.  At  a  higher  temperature,  the 
tension  is  raised,  as  there  is  a  greater  tendency  at  a  high  temperature  for 
the  chemical  compound  to  undergo  dissociation.  It  is  therefore  easy  to 
see  that  the  oxygen  tension  of  the  air  of  the  pulmonary  alveoli  is  quite 
sufficient,  even  supposing  it  much  less  than  that  of  the  expired  air,  to 
enable  the  venous  blood  to  take  up  oxygen,  and  what  is  more,  it  will  take 
it  up  until  the  haemoglobin  is  very  nearly  saturated  with  the  gas. 

As  regards  the  elimination  of  carbonic  acid  from  the  blood,  there  is 
evidence  to  show  that  it  is  given  up  by  a  process  of  simple  diffusion,  the 
only  condition  necessary  for  the  process  being  that  the  tension  of  the  car- 
tbonic  acid  of  the  air  in  the  pulmonary  alveoli  should  be  less  than  the  ten- 
sion of  the  carbonic  acid  in  venous  blood.  The  carbonic  acid  tension  of 
the  alveolar  air  probably  does  not  exceed  in  the  dog  3  or  4  per  cent., 
while  that  of  the  venous  blood  is  5 '4  per  cent.,  or  equal  to  41  mm.  of 
mercury. 

B.  Respiratory  Changes  in  the  Blood.  * 

Circulation  of  Blood  in  the  Respiratory  Organs. — To  be  ex-  )( 

posed  to  the  air  thus  alternately  moved  into  and  out  of  the  air  cells  and 
minute  bronchial  tubes,  the  blood  is  propelled  from  the  right  ventricle 


198  HAND-BOOK    OF    PHYSIOLOGY. 

through  the  pulmonary  capillaries  in  steady  streams,  and  slowly  enough 
to  permit  every  minute  portion  of  it  to  be  for  a  few  seconds  exposed  to 
the  air,  with  only  the  thin  walls  of  the  capillary  vessels  and  the  air-cells 
intervening.  The  pulmonary  circulation  is  of  the  simplest  kind:  for  the 
pulmonary  artery  branches  regularly;  its  successive  branches  run  in 
straight  lines,  and  do  not  anastomose:  the  capillary  plexus  is  uniformly 
spread  over  the  air-cells  and  intercellular  passages;  and  the  veins  derived 
from  it  proceed  in  a  course  as  simple  and  uniform  as  that  of  the  arteries, 
their  branches  converging  but  not  anastomosing.  The  veins  have  no- 
valves,  or  only  small  imperfect  ones  prolonged  from  their  angles  of  junc- 
tion, and  incapable  of  closing  the  orifice  of  either  of  the  veins  between 
which  they  are  placed.  The  pulmonary  circulation  also  is  unaffected  by 
changes  of  atmospheric  pressure,  and  is  not  exposed  to  the  influence  of 
the  pressure  of  muscles:  the  force  by  which  it  is  accomplished,  and  the 
course  of  the  blood,  are  alike  simple. 

Changes  produced  in  the  Blood  by  Respiration. — The  most 
obvious  change  which  the  blood  of  the  pulmonary  artery  undergoes  in 
its  passage  through  the  lungs  is  1st,  that  of  color,  the  dark  crimson  of 
venous  blood  being  exchanged  for  the  bright  scarlet  of  arterial  blood;  2nd, 
and  in  connection  with  the  preceding  change,  it  gains  oxygen;  3rd,  it 
loses  carbonic  acid;  tth,  it  becomes  slightly  cooler  (p.  193);  5th,  it  coagu- 
lates sooner  and  more  firmly,  and,  apparently,  contains  more  fibrin  (see 
p.  87).  The  oxygen  absorbed  into  the  blood  from  the  atmospheric  air 
in  the  lungs  is  combined  chemically  with  the  haemoglobin  of  the  red 
blood-corpuscles.  In  this  condition  it  is  carried  in  the  arterial  blood  to- 
the  various  parts  of  the  body,  and  brought  into  near  relation  or  contact 
with  the  tissues.  In  these  tissues,  and  in  the  blood  which  circulates  in, 
them,  a  certain  portion  of  the  oxygen,  which  the  arterial  blood  contains, 
disappears,  and  a  proportionate  quantity  of  carbonic  acid  and  water  is 
formed.  The  venous  blood,  containing  the  new-formed  carbonic  acid, 
returns  to  the  lungs,  where  a  portion  of  the  carbonic  acid  is  exhaled,  and 
a  fresh  supply  of  oxygen  is  taken  in. 

Mechanism  of  Various  Respiratory  Actions. — It  will  be  well 
here,  perhaps,  to  explain  some  respiratory  acts,  which  appear  at  first 
sight  somewhat  complicated,  but  cease  to  be  so  when  the  mechanism  by 
which  they  are  performed  is  clearly  understood.  The  accompanying  dia- 
gram (Fig.  161)  shows  that  the  cavity  of  the  chest  is  separated  from  that 
of  the  abdomen  by  the  diaphragm,  which,  when  acting,  will  lessen  its 
curve,  and  thus  descending,  will  push  downward  and  forward  the  ab- 
dominal viscera;  while  the  abdominal  muscles  have  the  opposite  effect, 
and  in  acting  will  push  the  viscera  upward  and  backward,  and  with 
them  the  diaphragm,  supposing  its  ascent  to  be  not  from  any  cause  inter- 
fered with.  From  the  same  diagram  it  will  be  seen  that  the  lungs  com- 
municate with  the  exterior  of  the  body  through  the  glottis,  and  further 


RESPIRATION.  199 

on  through  the  mouth  and  nostrils — through  either  of  them  separately, 
or  through  both  at  the  same  time,  according  to  the  position  of  the  soft 
palate.  The  stomach  communicates  with  the  exterior  of  the  body  through 
the  oesophagus,  pharynx,  and  mouth;  while  below  the  rectum  opens  at 
the  anus,  and  the  bladder  through  the  urethra.  All  these  openings, 
through  which  the  hollow  viscera  communicate  with  the  exterior  of  the 
body,  are  guarded  by  muscles,  called  sphincters,  which  can  act  independ- 
ently of  each  other.  The  position  of  the  latter  is  indicated  in  the  dia- 
gram. 


FIG.  161. 

Sighing. — In  sighing  there  is  a  rather  prolonged  inspiration;  the  air 
almost  noiselessly  passing  in  through  the  glottis,  and  by  the  elastic  recoil 
of  the  lungs  and  chest- walls,  and  probably  also  of  the  abdominal  walls, 
being  rather  suddenly  expelled  again. 

Now,  in  the  first,  or  inspiratory  part  of  this  act,  the  descent  of  the 
diaphragm  presses  the  abdominal  viscera  downward,  and  of  course  this 
pressure  tends  to  evacuate  the  contents  of  such  as  communicate  with  the 
exterior  of  the  body.  Inasmuch,  however,  as  their  various  openings  are 
guarded  by  sphincter  muscles,  in  a  state  of  constant  tonic  contraction, 


200  HAND-BOOK    OF    PHYSIOLOGY. 

there  is  no  escape  of  their  contents,  and  air  simply  enters  the  lungs.  In 
the  second,  or  expiratory  part  of  the  act  of  sighing,  there  is  also  pressure 
made  on  the  abdominal  viscera  in  the  opposite  direction,  by  the  elastic 
or  muscular  recoil  of  the  abdominal  walls;  but  the  pressure  is  relieved  by 
the  escape  of  air  through  the  open  glottis,  and  the  relaxed  diaphragm  is 
pushed  up  again  into  its  original  position.  The  sphincters  cf  the  stomach, 
rectum,  and  bladder,  act  as  before. 

Hiccough  resembles  sighing  in  that  it  is  an  inspiratory  act;  but  the 
inspiration  is  sudden  instead  of  gradual,  from  the  diaphragm  acting  sud- 
denly and  spasmodically;  and  the  air,  therefore,  suddenly  rushing  through 
the  unprepared  rima  glottidis,  causes  vibration  of  the  vocal  cords,  and 
the  peculiar  sound. 

Coughing. — In  the  act  of  coughing,  there  is  most  often  first  an  in- 
spiration, and  this  is  followed  by  an  expiration;  but  when  the  lungs  have 
been  filled  by  the  preliminary  inspiration,  instead  of  the  air  being  easily 
let  out  again  through  the  glottis,  the  latter  is  momentarily  closed  by  the 
approximation  of  the  vocal  cords,  and  then  the  abdominal  muscles, 
strongly  acting,  push  up  the  viscera  against  the  diaphragm,  and  thus 
make  pressure  on  the  air  in  the  lungs  until  its  tension  is  sufficient  to 
burst  open  noisily  the  vocal  cords  which  oppose  its  outward  passage.  In 
this  way  a  considerable  force  is  exercised,  and  mucus  or  any  other  matter 
that  may  need  expulsion  from  the  lungs  or  trachea  is  quickly  and  sharply 
expelled  by  the  outstreaming  current  of  air. 

Now  it  is  evident  on  reference  to  the  diagram  (Fig.  161),  that  pressure 
exercised  by  the  abdominal  muscles  in  the  act  of  coughing,  acts  as  for- 
cibly on  the  abdominal  viscera  as  on  the  lungs,  inasmuch  as  the  viscera 
form  the  medium  by  which  the  upward  pressure  on  the  diaphragm  is 
made,  and  of  necessity  there  is  quite  as  great  a  tendency  to  the  expulsion 
of  their  contents  as  of  the  air  in  the  lungs.  The  instinctive,  and  if 
necessary,  voluntarily  increased  contraction  of  the  sphincters,  however, 
prevents  any  escape  at  the  openings  guarded  by  them,  and  the  pressure  is 
effective  at  one  part  only,  namely,  the  rima  glottidis. 

Sneezing. — The  same  remarks  that  apply  to  coughing,  are  almost 
exactly  applicable  to  the  act  of  sneezing;  but  in  this  instance  the  blast 
of  air,  on  escaping  from  the  lungs,  is  directed,  by  an  instinctive  con- 
traction of  the  pillars  of  the  fauces  and  descent  of  the  soft  palate,  chiefly 
through  the  nose,  and  any  offending  matter  is  thence  expelled. 

Speaking. — In  speaking,  there  is  a  voluntary  expulsion  of  air  through 
the  glottis  by  means  of  the  expiratory  muscles;  and  the  vocal  cords  are 
put,  by  the  muscles  of  the  larynx,  in  a  proper  position  and  state  of  tension 
for  vibrating  as  the  air  passes  over  them,  and  thus  producing  sound.  The 
sound  is  moulded  into  words  by  the  tongue,  teeth,  lips,  etc. — the  vocal 
cords  producing  the  sound  only,  and  having  nothing  to  do  with  articu- 
lation. 


RESPIRATION.  201 

Singing. — Singing  resembles  speaking  in  the  manner  of  its  produc- 
tion; the  luryngetil  muscles,  by  variously  altering  the  position  and  degree 
of  tension  of  the  vocal  cords,  producing  the  different  notes.  Words  used 
in  the  act  of  singing  are  of  course  framed,  as  in  speaking,  by  the  tongue, 
teeth,  lips,  etc. 

Sniffing. — Sniffing  is  produced  by  a  somewhat  quick  action  of  the 
diaphragm  and  other  inspiratory  muscles.  The  mouth  is,  however,  closed, 
and  by  these  means  the  whole  stream  of  air  is  made  to  enter  by  the 
nostrils.  The  alge  nasi  are,  commonly,  at  the  same  time,  instinctively 
dilated. 

Sobbing. — Sobbing  consists  in  a  series  of  convulsive  inspirations,  at 
the  moment  of  which  the  glottis  is  usually  more  or  less  closed. 

Laughing. — Laughing  is  a  series  of  short  and  rapid  expirations. 

Yawning. — Yawning  is  an  act  of  inspiration,  but  is  unlike  most  of  the 
preceding  actions  in  being  always  more  or  less  involuntary.  It  is  attended 
by  a  stretching  of  various  muscles  about  the  palate  and  lower  jaw,  which 
is  probably  analogous  to  the  stretching  of  the  muscles  of  the  limbs  in 
which  a  weary  man  finds  relief,  as  a  voluntary  act,  when  they  have  been 
some  time  out  of  action.  The  involuntary  and  reflex  character  of  yawn- 
ing depends  probably  on  the  fact  that  the  muscles  concerned  are  them- 
selves at  all  times  more  or  less  involuntary,  and  require,  therefore, 
something  beyond  the  exercise  of  the  will  to  set  them  in  action.  For 
the  same  reason,  yawning,  like  sneezing,  cannot  be  well  performed 
voluntarily. 

Sucking. — Sucking  is  not  properly  a  respiratory  act,  but  it  may  be 
most  conveniently  considered  in  this  place.  It  is  caused  chiefly  by  the 
depressor  muscles  of  the  os  hyoides.  These,  by  drawing  downward  and 
backward  the  tongue  and  floor  of  the  mouth,  produce  a  partial  vacuum 
in  the  latter:  and  the  weight  of  the  atmosphere  then  acting  on  all  sides 
tends  to  produce  equilibrium  on  the  inside  and  outside  of  the  mouth  as 
best  it  may.  The  communication  between  the  mouth  and  pharynx  is 
completely  shut  off  by  the  contraction  of  the  pillars  of  the  soft  palate  and 
descent  of  the  latter  so  as  to  touch  the  back  of  the  tongue;  and  the  equi- 
librium, therefore,  can  be  restored  only  by  the  entrance  of  something 
through  the  mouth.  The  action,  indeed,  of  the  tongue  and  floor  of  the 
mouth  in  sucking  may  be  compared  to  that  of  the  piston  in  a  syringe, 
and  the  muscles  which  pull  down  the  os  hyoides  and  tongue,  to  the  power 
which  draws  the  handle. 

Influence  of  the  Nervous  System  in  Respiration.— Like  all 
other  functions  of  the  body,  the  discharge  of  which  is  necessary  to  life, 
respiration  must  be  essentially  an  involuntary  act.  Else,  life  would  be  in 
constant  danger,  and  would  cease  on  the  loss  of  consciousness  for  a  few 
moments,  as  in  sleep.  But  it  is  also  necessary  that  respiration  should  be 
to  some  extent  under  the  control  of  the  will.  For  were  it  not  so,  it  would 

4 


202  HAND-BOOK    OF    PHYSIOLOGY. 

be  impossible  to  perform  those  voluntary  respiratory  acts  which  have  been 
•just  enumerated  and  explained,  as  speaking,  singing,  and  the  like. 

The  respiratory  movements  and  their  rhythm,  so  far  as  they  are  invol- 
untary and  independent  of  consciousness  (as  on  all  ordinary  occasions)  are 
under  the  governance  of  a  nerve-centre  in  the  medulla  oblongata  correspond- 
ing with  the  origin  of  the  pneumogastric  nerves;  that  is  to  say,  the  motor 
nerves,  and  through  them  the  muscles  concerned  in  the  respiratory  move- 
ments, are  excited  by  a  stimulus  which  issues  from  this  part  of  the  nerv- 
ous system.  How  far  the  medulla  acts  automatically,  i.e.,  how  far  the 
stimulus  originates  in  it,  or  how  far  it  is  merely  a  nerve-centre  for  reflex 
action,  is  not  certainly  known.  Probably,  as  will  be  seen,  both  events 
happen;  and,  in  both  cases,  the  stimulus  is  the  result  of  the  condition  of 
the  blood. 

The  respiratory  centre  is  bilateral  or  double,  since  the  respiratory 
movements  continue  after  the  medulla  at  this  point  is  divided  in  the  mid- 
dle line. 

As  regards  its  supposed  automatic  action,  it  has  been  shown  that  if 
the  spinal  cord  be  divided  below  the  medulla,  and  both  vagi  be  divided 
so  that  no  afferent  impulses  can  reach  it  from  below,  the  nasal  and  laryn- 
geal  respiration  continues,  and  the  only  possible  course  of  the  afferent  im- 
pulses would  be  through  the  cranial  nerves;  and  when  the  cord  and  me- 
dulla are  intact  the  division  of  these  produces  no  effect  upon  respiration, 
so  that  it  appears  evident  that  the  afferent  stimuli  are  not  absolutely 
necessary  for  maintaining  the  respiratory  movements.  But  although  au- 
tomatic in  its  action  the  respiratory  centre  may  be  reflexly  excited,  and  the 
chief  channel  of  this  reflex  influence  is  the  vagus  nerve;  for  when  the 
nerve  of  one  side  is  divided,  respiration  is  slowed,  and  if  both  vagi  be  cut 
the  respiratory  action  is  still  slower. 

The  influence  of  the  vagus  trunk  upon  it  is  twofold,  for  if  the  nerve 
be  divided  below  the  origin  of  the  superior  laryngeal  branch  and  the  cen- 
tral end  be  stimulated,  respiratory  movements  are  increased  in  rapidity, 
and  indeed  follow  one  another  so  quickly  if  the  stimuli  be  increased  in 
number,  that  after  a  time  cessation  of  respiration  in  inspiration  follows 
from  a  tetanus  of  the  respiratory  muscles  (diaphragm).  Whereas  if  the 
superior  laryngeal  branch  be  divided,  although  no  effect,  or  scarcely  any, 
follows  the  mere  division,  on  stimulation  of  the  central  end  respiration 
is  slowed,  and  after  a  time,  if  the  stimulus  be  increased,  stops,  but  not  in 
inspiration  as  in  the  other  case,  but  in  expiration.  Thus  the  vagus  trunk 
contains  fibres  which  slow  and  fibres  which  accelerate  respiration.  If  we 
adopt  the  theory  of  a  doubly  acting  respiratory  centre  in  the  floor  of  the 
medulla,  one  tending  to  produce  inspiration  and  the  other  expiration, 
and  acting  in  antagonism  as  it  were,  so  that  there  is  a  gradual  increase  in 
the  tendency  to  produce  respiratory  action,  until  it  culminates  in  an  in- 
spiratory  effort,  which  is  followed  by  a  similar  action  of  the  expiratory 


RESPIRATION.  203 

part  of  the  centre,  producing  an  expiration,  we  must  look  upon  the  main 
trunk  of" the  vagus  as  aiding  the  inspiratory,  and  of  the  superior  laryngeal 
as  aiding  the  expiratory  part  of  the  centre,  the  first  nerve  possibly  in- 
hibiting the  action  of  the  expiratory  centre,  whilst  it  aids  the  inspiratory, 
and  the  latter  nerve  having  the  very  opposite  effect.  But  inasmuch  as 
the  respiration  is  slowed  on  division  of  the  vagi,  and  not  quickened  or 
affected  manifestly  on  simple  division  of  the  superior  laryngeal,  it  must 
be  supposed  that  the  vagi  fibres  are  always  in  action,  whereas  the  superior 
laryngeal  fibres  are  not. 

It  appears,  however,  that  there  are,  in  some  animals  at  all  events, 
subordinate  centres  in  the  spinal  cord  which  are  able,  under  certain  con- 
ditions, to  discharge  the  function  of  the  chief  medullary  centre. 

The  centre  in  the  medulla  may  be  influenced  not  only  by  afferent  im- 
pulses proceeding  along  the  vagus  and  laryngeal  nerves  but  also  by  those 
proceeding  from  the  cerebrum,,  as  well  as  by  impressions  made  upon  the 
nerves  of  the  skin,  or  upon  part  of  the  fifth  nerve  distributed  to  the  nasal 
mucous  membrane,  or  upon  other  sensory  nerves,  as  is  exemplified  by 
the  deep  inspiration  which  follows  the  application  of  cold  to  the  surface 
of  the  skin,  and  by  the  sneezing  which  follows  the  slightest  irritation  of 
the  nasal  mucous  membrane. 

At  the  time  of  birth,  the  separation  of  the  placenta,  and  the  conse- 
quent non-oxygenation  of  the  foetal  blood,  are  the  circumstances  which 
immediately  lead  to  the  issue  of  automatic  impulses  to  action  from  the 
respiratory  centre  in  the  medulla  oblongata.  But  the  quickened  action 
which  ensues  on  the  application  of  cold  air  or  water,  or  other  sudden 
stimulus,  to  the  skin,  shows  well  the  intimate  connection  which  exists 
between  this  centre  and  other  parts  which  are  not  ordinarily  connected 
with  the  function  of  respiration. 

Methods  of  Stimulation  of  the  Respiratory  Centre.— It  is  now 

necessary  to  consider  the  method  by  which  the  centre  or  centres  are  stim- 
ulated themselves,  as  well  as  the  manner  in  which  the  afferent  vagi 
impulses  are  produced. 

The  more  venous  the  blood,  the  more  marked  are  the  inspiratory  im- 
pulses, and  if  the  air  is  prevented  from  entering  the  chest,  in  a  short  time 
the  respiration  becomes  very  labored.  Its  cessation  is  followed  by  an 
abnormal  rapidity  of  the  inspiratory  acts,  which  make  up  even  in  depth 
for  the  previous  stoppage.  The  condition  caused  by  obstruction  to  the 
entrance  of  air,  or  by  any  circumstance  by  which  the  oxygen  of  the  blood 
is  used  up  in  an  abnormally  quick  manner,  is  known  as  dyspnaa,  and  as 
the  aeration  of  the  blood  becomes  more  and  more  interfered  with,  not 
only  are  the  ordinary  respiratory  muscles  employed,  but  also  those  extra- 
ordinary muscles  which  have  been  previously  enumerated  (p.  186),  so  that 
as  the  blood  becomes  more  and  more  venous  the  action  of  the  medullary 
centre  becomes  more  and  more  active.  The  question  arises  as  to  what 


204 


HAND-BOOK    OF    PHYSIOLOGY. 


condition  of  the  venous  bbod  causes  this  increased  activity,  whether  it 
is  due  to  deficiency  of  oxygen  or  excess  of  carbonic  acid  in  the  blood. 
This  has  been  answered  by  the  experiments,  which  show  on  the  one  hand 
that  dyspnoea  occurs  when  there  is  no  obstruction  to  the  exit  of  carbonic 
acid,  as  when  an  animal  is  placed  in  an  atmosphere  of  nitrogen,  and 
therefore  cannot  be  due  to  the  accumulation  of  carbonic  acid,  and  sec- 
ondly, that  if  plenty  of  oxygen  be  supplied,  dyspnoea  proper  does  not. 
occur,  although  the  carbonic  acid  of  the  blood  is  in  excess.  The  respir- 
atory centre  is  evidently  stimulated  to  action  by  the  absence  of  sufficient 
oxygen  in  the  blood  circulating  in  it. 

The  method  by  which  the  vagus  is  stimulated  to  conduct  afferent  im- 
pulses, influencing  the  action  of  the  respiratory  centre,  appears  to  be  by 
the  venous  blood  circulating  in  the  lungs,  or  as  some  say  by  the  condition 
of  the  air  in  the  pulmonary  alveoli.  And  if  either  of  these  be  the  stimuli 
it  will  be  evident  that  as  the  condition  of  venous  blood  stimulates  the 
peripheral  endings  of  the  vagus  in  the  lungs,  the  vagus  action  which  tends 
to  help  oil  the  discharge  of  inspiratory  impulses  from  the  centre,  must 
tend  also  to  increase  the  activity  of  the  centre,  when  the  blood  in  the 
lungs  becomes  more  and  more  venous.  No  doubt  the  venous  condition 
of  the  blood  will  affect  all  the  sensory  nerves  in  a  similar  manner,  but  it 
has  been  shown  that  the  circulation  of  too  little  blood  through  the 
centre  is  quite  sufficient  by  itself  for  the  purpose;  as  when  its  blood  sup- 
ply is  cut  off  increased  inspiratory  actions  ensue. 

Effects  of  Vitiated  Air. — Ventilation.— We  have  seen  that  the 
air  expired  from  the  lungs  contains  a  large  proportion  of  carbonic  acid 
and  a  minute  amount  of  organic  putrescible  matter. 

Hence  it  is  obvious  that  if  the  same  air  be  breathed  again  and  again, 
the  proportion  of  carbonic  acid  and  organic  matter  will  constantly  increase 
till  fatal  results  are  produced;  but  long  before  this  point  is  reached, 
uneasy  sensations  occur,  such  as  headache,  languor,  and  a  sense  of  oppres- 
sion. It  is  a  remarkable  fact  that  the  organism  after  a  time  adapts  itself 
to  such  a  vitiated  atmosphere,  and  that  a  person  soon  comes  to  breathe, 
without  sensible  inconvenience,  an  atmosphere  which,  when  he  first 
entered  it,  felt  intolerable.  Such  an  adaptation,  however,  can  only  take 
place  at  the  expense  of  a  depression  of  all  the  vital  functions,  which  must 
be  injurious  if  long  continued  or  often  repeated. 


This  power  of  adaptation  is  well  illustrated  by  the  experiments  of 
Claude  Bernard.  A  sparrow  is  placed  under  a  bell-glass  of  such  a  size 
that  it  will  live  for  three  hours.  If  now  at  the  end  of  the  second  hour 
(when  it  could  have  survived  another  hour)  it  be  taken  out  and  a  fresh 
healthy  sparrow  introduced,  the  latter  will  perish  instantly. 

The  adaptation  above  spoken  of  is  a  gradual  and  continuous  one:  thus 
a  bird  which  will  live  one  hour  in  a  pint  of  air  will  live  three  hours  in 
two  pints;  and  if  two  birds  of  the  same  species,  age,  and  size,  be  placed 


RESPIRATION. 


205 


a  quantity  of  air  in  which  either,  separately,  would   survive   three 
>urs,  they  will  not  live  1£  hour,  but  only  1£  hour. 

From  what  has  been  said  it  must  be  evident  that  provision  for  a  con- 
it  and  plentiful  supply  of  fresh  air,  and  the  removal  of  that  which  is 

itiaU'd,  is  of  far  greater  importance  than  the  actual  cubic  space  per  head 
occupants.  Not  less  than  2000  cubic  feet  per  head  should  be  allowed 
sleeping  apartments  (barracks,  hospitals,  etc.),  and  with  this  allow- 
the  air  can  only  be  maintained  at  the  proper  standard  of  purity  by 

ich  a  system  of  ventilation  as  provides  for  the  supply  of  1500  to  2000 

ibic  feet  of  fresh  air  per  head  per  hour.     (Parkes.) 

THE  EFFECT  OF  RESPIRATION  ON  THE  CIRCULATION. 

Inasmuch  as  the  heart  and  great  vessels  are  situated  in  the  air-tight 
lorax,  they  are  exposed  to  a  certain  alteration  of  pressure  when  the 


FIG.  162. — Diagram  of  an  apparatus  illustrating  the  effect  of  inspiration  upon  the  heart  and  great 
vessels  within  the  thorax.— I,  the  thorax  at  rest;  If,  during  inspiration:  p,  represents  the  diaphragm 
when  relaxed;  D'  when  contracted  (it  must  be  remembered  that  this  position  is  a  mere  diagram),  i.  e., 
when  the  capacity  of  the  thorax  is  enlarged;  H,  the  heart;  v,  the  veins  entering  it,  and  A,  the  aorta; 
R/.  Ll,  the  right  and  left  lung;  T,  the  trachea;  M,  mercurial  manometer  in  connection  with  the  pleura. 
The  increase  in  the  capacity  of  the  box  representing  the  thorax  is  seen  to  dilate  the  heart  as  well  as 
the  lungs,  and  so  to  pump  in  blood  through  v,  whereas  the  valve  prevents  reflex  through  A.  The 
position  of  the  mercury  in  M  shows  also  the  suction  which  is  taking  place.  (Landois.) 

capacity  of  the  latter  is  increased;  for  although  the  expansion  of  the 
lungs  during  inspiration  tends  to  counterbalance  this  increase  of  area,  it 
never  quite  does  so,  since  part  of  the  pressure  of  the  air  which  is  drawn 


206  HAND-BOOK    OF    PHYSIOLOGY. 

into  the  chest  through  the  trachea  is  expended  in  overcoming  the  elas- 
ticity of  the  lungs  themselves.  The  amount  thus  used  up  increases  as 
the  lungs  become  more  and  more  expanded,  so  that  the  pressure  inside 
the  thorax  during  inspiration  as  far  as  the  heart  and  great  vessels  are  con- 
cerned, never  quite  equals  that  outside,  and  at  the  conclusion  of  inspira- 
tion is  considerably  less  than  the  atmospheric  pressure.  It  has  been  ascer- 
tained that  the  amount  of  the  pressure  used  up  in  the  way  above  described, 
varies  from  5  or  7  mm.  of  mercury  during  the  pause,  and  to  30  mm.  of 
mercury  when  the  lungs  are  expanded  at  the  end  of  a  deep  inspiration, 
so  that  it  will  be  understood  that  the  pressure  to  which  the  heart  and 
great  vessels  are  subjected  diminishes  as  inspiration  progresses.  It  will 
be  understood  from  the  accompanying  diagram  how,  if  there  wrere  no 
lungs  in  the  chest,  but  if  its  capacity  were  increased,  the  effect  of  the 
increase  would  be  expended  in  pumping  blood  into  the  heart  from  the 
veins,  but  even  with  the  lungs  placed  as  they  are,  during  inspiration  the 
pressure  outside  the  heart  and  great  vessels  is  diminished,  and  they  have 
therefore  a  tendency  to  expand  and  to  diminish  the  intra-vascular  pres- 
sure. The  diminution  of  pressure  within  the  veins  passing  to  the  right 
auricle  and  within  the  right  auricle  itself,  will  draw  the  blood  into  the 
thorax,  and  so  assist  the  circulation:  this  suction  action  aiding,  though 
independently,  the  suction  power  of  the  diastole  of  the  auricle  about 
which  we  have  previously  spoken  (p.  124).  The  effect  of  sucking  more 
blood  into  the  right  auricle  will,  cceteris  paribus,  increase  the  amount 
passing  through  the  right  ventricle,  which  also  exerts  a  similar  suction 
action,  and  througji  the  lungs  into  the  left  auricle  and  ventricle  and  thus 
into  the  aorta,  and  this  tends  to  increase  the  arterial  tension.  The  effect 
of  the  diminished  pressure  upon  the  pulmonary  vessels  will  also  help 
toward  the  same  end,  i.e.,  an  increased  flow  through  the  lungs,  so  that  as 
far  as  the  heart  and  its  veins  are  concerned  inspiration  increases  the  blood 
pressure  in  the  arteries.  The  effect  of  inspiration  upon  the  aorta  and  its 
branches  within  the  thorax  would  be,  however,  contrary;  for  as  the 
pressure  outside  is  diminished  the  vessels  would  tend  to  expand,  and  thus 
to  diminish  the  tension  of  the  blood  within  them,  but  inasmuch  as  the 
large  arteries  are  capable  of  little  expansion  beyond  their  natural  calibre, 
the  diminution  of  the  arterial  tension  caused  by  this  means  would  be  in- 
sufficient to  counteract  the  increase  of  arterial  tension  produced  by  the 
effect  of  inspiration  upon  the  veins  of  the  chest,  and  the  balance  of  the 
whole  action  would  be  in  favor  of  an  increase  of  arterial  tension  during 
the  inspiratory  period.  But  if  a  tracing  of  the  variation  be  taken  at  the 
same  time  that  the  respiratory  movements  are  recorded,  it  will  be  found 
that,  although  speaking  generally,  the  arterial  tension  is  increased  during 
inspiration,  the  maximum  of  arterial  tension  does  not  correspond  with 
the  acme  of  inspiration  (Fig.  163). 

As  regards  the  effect  of  expiration,  the  capacity  of  the  chest  is  dimin- 


RESPIRATION. 


•207 


ished,  and  the  intra-thoracic  pressure  returns  to  the  normal,  which  is 
not  exactly  equal  to  the  atmospheric,  pressure.  The  effect  of  this  on  the 
veins  is  to  increase  their  intra-vascular  pressure,  and  so  to  diminish  the 
flow  of  blood  into  the  left  side  of  the  heart,  and  with  it  the  arterial  ten- 
sion, but  this  is  almost  exactly  balanced  by  the  necessary  increase  of 
arterial  tension  caused  by  the  increase  of  the  extra-vascular  pressure  of 
the  aorta  and  large  arteries,  so  that  the  arterial  tension  is  not  much 
affected  during  expiration  either  way.  Thus,  ordinary  expiration  does 


one  limb  of  a  manometer  with  the  pleural  cavity.  Inspiration  begins  at  i  and  expiration  at  e.  The 
intra-thoracic  pressure  rises  very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and  then  slow- 
ly falls  as  the  air  issues  from  the  chest;  at  the  beginning  of  the  inspiratory  effort  the  fall  becomes 
more  rapid.  (M.  Foster.) 

» 

not  produce  a  distinct  obstruction  to  the  circulation,  as  even  when  the 
expiration  is  at  an  end  the  intra-thoracic  pressure  is  less  than  the  extra- 
thoracic. 

The  effect  of  violent  expiratory  efforts,  however,  has  a  distinct  action 
in  preventing  the  current  of  blood  through  the  lungs,  as  seen  in  the 
blueness  of  the  face  from  congestion  in  straining;  this  condition  being 
produced  by  pressure  on  the  small  pulmonary  vessels. 

We  may  summarize  this  mechanical  effect,  therefore,  and  say  that  in- 
spiration aids  the  circulation  and  so  increases  the  arterial  tension,  and 
that  although  expiration  does  not  materially  aid  the  circulation,  yet  under 
ordinary  conditions  neither  does  it  obstruct.  Under  extraordinary  con- 
ditions, as  in  violent  expirations,  the  circulation  is  decidedly  obstructed. 
But  we  have  seen  that  there  'IB  no  exact  correspondence  between  the 
points  of  extreme  arterial  tension  and  the  end  of  inspiration,  and  we  must 
look  to  the  nervous  system  for  an  explanation  of  this  apparently  contra- 
dictory result. 

The  effect  of  the  nervous  system  in  producing  a  rhythmical  alteration 
of  the  blood  pressure  is  twofold.  In  the  first  place  the  cardw-inliibitory 
centre,  is  believed  to  be  stimulated  during  the  fall  of  blood  pressure,  pro- 


208 


HAND-BOOK    OF    PHYSIOLOGY. 


ducing  a  slower  rate  of  heart-beats  during  expiration,  which  will  be 
noticed  in  the  tracing  (Fig.  163),  the  undulations  during  the  decline  of 
blood-pressure  being  longer  but  less  frequent.  This  effect  disappears 
when,  by  section  of  the  vagi,  the  effect  of  the  centre  is  cut  off  from  the 
heart.  In  the  second  place,  the  vaso-motor  centre  is  also  believed  to  send 
out  rhythmical  impulses,  by  which  undulations  of  blood  pressure  are  pro- 
duced independently  of  the  mechanical  effects  of  respiration. 


FIG.  164.— Traube-Hering's  curves.  (To  be  read  from  left  to  right.)  The  curves  1,  2,  3,  4,  and  5 
are  portions  selected  from  one  continuous  tracing  forming  the  record  of  a  prolonged  observation,  so 
that  the  several  curves  represent  successive  stages  of  the  same  experiment.  Each  curve  is  placed  in 
its  proper  position  relative  to  the  base  line,  which  is  omitted;  the  blood-pressure  rises  in  stages  from 
1,  to  2,  3,  and  4,  but  falls  again  in  stage  5.  Curve  1  is  taken  from  a  period  when  artificial  respiration 
was  being  kept  up,  but  the  vagi  having  been  divided,  the  pulsations  on  the  ascent  and  descent  of  the 
undulations  do  not  differ;  when  artificial  respiration  ceased  these  undulations  for  a  while  disappeared, 
and  the  blood-pressure  rose  steadily  while  the  heart-beats  became  slower.  Soon,  as  at  2,  new  un- 
dulations appeared ;  a  little  later,  the  blood-pressure  was  still  rising,  the  heart-beats  still  slower,  but 
the  undulations  still  more  obvious  (3):  still  later  (4),  the  pressure  was  still  higher,  but  the  heart-beats 
were  quicker,  and  the  undulations  flatter,  the  pressure  then  began  to  fall  rapidly  (5),  and  continued 
to  fall  until  some  time  after  artificial  respiration  was  resumed.  (M.  Foster.) 

The  action  of  the  vaso-motor  centre  in  taking  part  in  producing 
rhythmical  changes  of  blood-pressure  which  are  called  respiratory,  is 
shown  in  the  following  way: — In  an  animal  under  the  influence  of  urari, 
record  of  whose  blood-pressure  is  being  taken,  and  where  artificial  respi- 
ration has  been  stopped,  and  both  vagi  cut,  the  blood-pressure  curve  rises 
at  first  almost  in  a  straight  line;  but  after  a  time  new  rhythmical  undula- 
tions occur  very  like  the  original  respiratory  undulatious,  only  somewhat 


RESPIRATION.  209 

larger.  These  are  called  Traubes  or  Traube- Her  ing's  curves.  They  con- 
tinue whilst  the  blood-pressure  continues  to  rise,  and  only  cease  when  the 
vaso-motor  centre  and  the  heart  are  exhausted,  when  the  pressure  speedily 
falls.  These  .curves  must  be  dependent  upon  the  vaso-motor  centre,  as 
the  mechanical  effects  of  respiration  have  been  eliminated  by  the  poison 
and  by  the  cessation  of  artificial  respiration,  and  the  effect  of  the  cardio- 
inhibitory  centre  be  the  division  of  the  vagi.  It  may  be  presumed  there- 
fore that  the  vaso-motor  centre,  as  well  as  the  cardio-inhibitory,  must  be 
considered  to  take  part  with  the  mechanical  changes  of  inspiration  and 
expiration  in  producing  the  so-called  respiratory  undulations  of  blood- 
pressure. 

Cheyne- Stokes' s  breathing. — This  is  a  rhythmical  irregularity  in  respi- 
rations which  has  been  observed  in  various  diseases,  and  is  especially  con- 
nected with  fatty  degeneration  of  the  heart.  Respirations  occur  in  groups, 
at  the  beginning  of  each  group  the  inspirations  are  very  shallow,  but  each 
successive  breath  is  deeper  than  the  preceding  until  a  climax  is  reached, 
then  comes  in  a  prolonged  sighing  expiration,  succeeded  by  a  pause,  after 
which  the  next  group  begins. 

AP^CE  A.  — D  YSP:NXE  A.  — ASPHYXIA. 

As  blood  which  contains  a  normal  proportion  of  oxygen  excites  the 
respiratory  centre  (p.  204),  and  as  the  excitement  and  consequent  respir- 
atory muscular  movements  are  greater  (dyspnoea)  in  proportion  to  the 
deficiency  of  this  gas,  so  an  abnormally  large  proportion  of  oxygen  in  the 
blood  leads  to  diminished  breathing  movements,  and,  if  the  proportion  be 
large  enough,  to  their  temporary  cessation.  This  condition  of  absence  of 
breathing  is  termed  apncea,1  and  it  can  be  demonstrated,  in  one  of  the 
lower  animals,  by  performing  artificial  respiration  to  the  extent  of  satura- 
ting the  blood  with  oxygen. 

When,  on  the  other  hand,  the  respiration  is  stopped,  by,  e.g., 
interference  with  the  passage  of  air  to  the  lungs,  or  by  supplying  air 
devoid  of  oxygen,  a  condition  ensues,  which  passes  rapidly  from  the  state 
of  dyspnoea  (difficult  breathing)  to  what  is  termed  asphyxia;  and  the 
latter  quickly  ends  in  death. 

The  ways  by  which  this  condition  of  asphyxia  may  be  produced  are 
very  numerous;  as,  for  example,  by  the  prevention  of  the  due  entry  of 
oxygen  into  the  blood,  either  by  direct  obstruction  of  the  trachea  or  other 
part  of  the  respiratory  passages,  or  by  introducing  instead  of  ordinary  air 
a  gas  devoid  of  oxygen,  or,  again,  by  interference  with  the  due  inter- 
change of  gases  between  the  air  and  the  blood. 

Symptoms  of  Asphyxia. — The  most  evident  symptoms  of  asphyxia 
or  suffocation  are  well  known.  Violent  action  of  the  respiratory  muscles 

1  This  term  has  been,  unfortunately,  often  applied  to  conditions  of  dyspncea  or 
asphyxia;  but  the  modern  application  of  the  term,  as  in  the  text,  is  the  more  convenient. 
VOL.  I.— 14. 


210  HAND-BOOK    OF    PHYSIOLOGY. 

and,  more  or  less,  of  all  the  muscles  of  the  body;  lividity  of  the  skin  and 
all  other  vascular  parts,  while  the  veins  are  also  distended,  and  the  tissues 
seem  generally  gorged  with  blood;  convulsions,  quickly  followed  by  in- 
sensibility, and  death. 

The  conditions  which  accompany  these  symptoms  are — 

(1)  More  or  less  interference  with  the  passage  of  the  blood  through 
the  pulmonary  blood-vessels. 

(2)  Accumulation  of  blood  in  the  right  side  of  the  heart  and  in  the 
systemic  veins. 

(3)  Circulation  of  impure  (non-aerated)  blood  in  all  parts  of  the  body. 
Cause  of  Death  from  Asphyxia.— The  causes  of  these  conditions 

and  the  manner  in  which  they  act,  so  as  to  be  incompatible  with  life,  may 
be  here  briefly  considered. 

(1)  The  obstruction  to  the  passage  of  blood  through  the  lungs  is  not 
so  great  as  it  was  once  supposed  to  be;  and  such  as  there  is  occurs  chiefly 
in  the  later  stages  of  asphyxia,  when,  by  the  violent  and  convulsive  action 
of  the  expiratory  muscles,  pressure  is  indirectly  made  on  the  lungs,  and 
the  circulation  through  them  is  proportionately  interfered  with. 

(2)  Accumulation  of  blood,  with  consequent  distension  of  the  right 
side  of  the  heart  and  systemic  veins,  is  the  direct  result,  at  least  in  part, 
of  the  obstruction  to  the  pulmonary  circulation  just  referred  to.     Other 
causes,  however,  are  in  operation,     (a)  The  vaso-motor  centres  stimu- 
lated by  blood  deficient  in  oxygen,  causes  contraction  of  all  the  small 
arteries  with  increase  of  arterial  tension,  and  as  an  immediate  conse- 
quence the  filling  of  the  systemic  veins,     (b)  The  increased  arterial  ten- 
sion is  followed  by  inhibition  of  the  action  of  the  heart,  and,  thus,  the 
latter,  contracting  less  frequently,  and  gradually  enfeebled  also  by  defi- 
cient supply  of  oxygen,  becomes  over-distended  by  blood  which  it  cannot 
expel.     At  this  stage  the  left  as  well  as  the  right  cavities  are  distended 
with  blood. 

The  ill  effects  of  these  conditions  are  to  be  looked  for  partly  in  the  heart, 
the  muscular  fibres  of  which,  like  those  of  the  urinary  bladder  or  any 
other  hollow  muscular  organ,  may  be  paralyzed  by  over-stretching;  and 
partly  in  the  venous  congestion,  and  consequent  interference  with  the 
function  of  the  higher  nerve-centres,  especially  the  medulla  oblongata. 

(3)  The  passage  of  non-aerated  blood  through  the  lungs  and  its  dis- 
tribution over  the  body  are  events  incompatible  with  life,  in  one  of  the 
higher  animals,  for  more  than  a  few  minutes;  the  rapidity  with  which 
death  ensues  in  asphyxia  being  due,  more  particularly,  to  the  effect  of 
non-oxygenized  blood  on  the  medulla  oblongata,  and,  through  the  coro- 
nary arteries,  on  the  muscular  substance  of  the  heart.     The  excitability 

.of  both  nervous  and  muscular  tissue  is  dependent  on  a  constant  and  large 
supply  of  oxygen,  and,  when  this  is  interfered  with,  is  rapidly  lost.  The 
diminution  of  oxygen,  it  may  be  here  remarked,  has  a  more  direct  in- 


RESPIRATION.  211 

luence  in  the  production  of  the  usual  symptoms  of  asphyxia  than  the 
icreased  amount  of  carbonic  acid.  Indeed,  the  fatal  effect  of  a  gradual 
emulation  of  the  latter  in  the  blood,  if  a  due  supply  of  oxygen  be 
luintuined,  resembles  rather  that  of  a  narcotic  poison. 

In  some  experiments  performed  by  a  committee  appointed  by  the 
[edico-Chirurgical  Society  to  investigate  the  subject  of  Suspended  Ani- 
latioti,  it  was  found  that,  in  the  dog,  during  simple  asphyxia,  i.e.,  by 
simple  privation  of  air,  as  by  plugging  the  trachea,  the  average  duration 
)f  the  respiratory  movements  after  the  animal  had  been  deprived  of  air, 
ras  4  minutes  5  seconds;  the  extremes  being  3  minutes  30  seconds,  and 
minutes  40  seconds.     The  average  duration  of  the  heart's  action,  on  the 
)therliand,  was  7  minutes  11  seconds;  the  extremes  being  6  minutes  40 
nets,  and  7  minutes  45  seconds.     It  would  seem,  therefore,  that  on 
an  average,  the  heart's  action  continues  for  3  minutes  15  seconds  after  the 
minril  has  ceased  to  make  respiratory  eiforts.     A  very  similar  relation 
was  observed  in  the  rabbit.     Recovery  never  took  place  after  the  heart's 
action  had  ceased. 

The  results  obtained  by  the  committee  on  the  subject  of  drowning 
were  very  remarkable,  especially  in  this  respect,  that  whereas  an  animal 
may  recover,  after  simple  deprivation  of  air  for  nearly  four  minutes,  yet, 
after  submersion  in  water  for  1|  minute,  recovery  seems  to  be  impossible. 
This  remarkable  difference  was  found  to  be  due,  not  to  the  mere  submer- 
sion, nor  directly  to  the  struggles  of  the  animal,  nor  to  depression  of  tem- 
perature, but  to  the  two  facts,  that  in  drowning,  a  free  passage  is  allowed 
to  air  out  of  the  lungs,  and  a  free  entrance  of  water  into  them.  It  is 
probably  to  the  entrance  of  water  into  the  lungs  that  the  speedy  death  in 
drowning  is  mainly  due.  The  results  of  post-mortem  examination  strongly 
support  this  view.  On  examining  the  lungs  of  animals  deprived  of  air 
by  plugging  the  trachea,  they  were  found  simply  congested;  but  in  the 
animals  drowned,  not  only  was  the  congestion  much  more  intense,  accom- 
panied with  ecchymosed  points  on  the  surface  and  in  the  substance  of 
the  lung,  but  the  air  tubes  were  completely  choked  up  with  a  sanious 
foam,  consisting  of  blood,  water,  and  mucus,  churned  up  with  the  air  in 
the  lungs  by  the  respiratory  efforts  of  the  animal.  The  lung-substance, 
too,  appeared  to  be  saturated  and  sodden  with  water,  which,  stained 
slightly  with  blood,  poured  out  at  any  point  where  a  section  was  made. 
The  lung  thus  sodden  with  water  was  heavy  (though  it  floated),  doughy, 
pitted  on  pressure,  and  was  incapable  of  collapsing.  It  is  not  difficult  to 
understand  how,  by  such  infraction  of  the  tubes,  air  is  debarred  from 
iva ehing  the  pulmonary  cells;  indeed  the  inability  of  the  lungs  to  collapse 
on  opening  the  chest  is  a  proof  of  the  obstruction  which  the  froth  occu- 
pying the  air-tubes  offers  to  the  transit  of  air. 

We  must  carefully  distinguish  the  asphyxiating  effect  of  an  insuffi- 
cient supply  of  oxygen  from  the  directly  poisonous  action  of  such  a  gas 
as  carbonic  oxide,  which  is  present  to  a  considerable  amount  in  common 
coal-gas.  The  fatal  effects  often  produced  by  this  gas  (as  in  accidents 
from  burning  charcoal  stoves  in  small,  close  rooms),  are  due  to  its  enter- 
ing into  combination  with  the  haemoglobin  of  the  blood -corpuscles 
(p.  95),  and  thus  expelling  the  oxygen. 


CHAPTER  VII. 

FOOD. 

IK  order  that  life  may  be  maintained  it  is  necessary  that  th%  body 
should  be  supplied  with  food  in  proper  quality  and  quantity. 

The  food  taken  in  by  the  animal  body  is  used  for  the  purpose  of  re- 
placing the  waste  of  the  tissues.  And  to  arrive  at  a  reasonable  estimation 
of  the  proper  diet  in  twenty-four  hours  it  is  necessary  to  consider  the 
amount  of  the  excreta  daily  eliminated  from  the  body.  The  excreta  con- 
tain chiefly  carbon,  hydrogen,  oxygen,  and  nitrogen,  but  also  to  a  less 
extent,  sulphur,  phosphorus,  chlorine,  potassium,  sodium,  and  certain 
other  of  the  elements.  Since  this  is  the  case  it  must  be  evident  that,  to 
balance  this  waste,  foods  must  be  supplied  containing  all  these  elements 
to  a  certain  degree,  and  some  of  them,  viz.,  those  which  take  the  prin- 
cipal part  in  forming  the  excreta,  in  large  amount.  We  have  seen  in  the 
last  Chapter  that  carbonic  acid  and  ammonia,  i.e.,  the  elements  carbon, 
oxygen,  nitrogen,  hydrogen,  are  given  off  from  the  lungs.  By  the  excre- 
tion of  the  kidneys — the  urine — many  elements  are  discharged  from  the 
blood,  especially  nitrogen,  hydrogen,  and  oxygen.  In  the  sweat,  the  ele- 
ments chiefly  represented  are  carbon,  hydrogen,  and  oxygen,  and  also  in 
the  faeces.  By  all  the  excretions  large  quantities  of  water  are  got  rid  of 
daily,  but  chiefly  by  the  urine. 

The  relations  between  the  amounts  of  the  chief  elements  contained 
in  these  various  excreta  in  twenty-four  hours  may  be  represented  in  the 
following  way  (Landois) : 

Water.  C.               H.  K  O. 

By  the  lungs     .         .       330  248-8            —  ?  651.15 

By  the  skin       .         .       660  2.6  7  '2 

By  the  urine     .         .     1700  9 -8  3*3  15-8  11-1 

By  the  faeces     .         .       128  20-  3'  3'  12 


Grammes    •         •     2818          281*2  6-3          18 -8          681-41 

To  this  should  be  added  296-  grammes  water,  which  are  produced  by 
the  union  of  hydrogen  and  oxygen  in  the  body  during  the  process  of  oxi- 
dation (i.e.,  32-89  hydrogen  and  263.41  oxygen).  There  are  twenty-six 
grammes  of  salts  got  rid  of  by  the  urine  and  six  by  the  fasces.  As  the 


FOOD. 


213 


water  can  be  supplied  as  such,  the  losses  of  carbon,  nitrogen,  and  oxygen 
are  those  to  which  we  should  direct  our  attention  in  supplying  food. 

For  the  sake  of  example,  we  may  now  take  only  two  elements,  carbon 
and  nitrogen,  and,  if  we  discover  what  amount  of  these  is  respectively  dis- 
charged in  a  given  time  from  the  body,  we  shall  be  in  a  position  to  judge 
what  kind  of  food  will  most  readily  and  economically  replace  their  loss. 

The  quantity  of  carbon  daily  lost  from  the  body  amounts  to  about 
281  '2  grammes  or  nearly  4,500  grains,  "and  of  nitrogen  18 '8  grammes  or 
nearly  300  grains;  and  if  a  man  could  be  fed  by  these  elements,  as  such, 
the  problem  would  be  a  very  simple  one;  a  corresponding  weight  of 
charcoal,  and,  allowing  for  the  oxygen  in  it,  of  atmospheric  air,  would  be 
all  that  is  necessary.  But  an  animal  can  live  only  upon  these  elements 
when  they  are  arranged  in  a  particular  manner  with  others,  in  the  form 
of  an  organic  compound,  as  albumen,  starch,  and  the  like;  and  the  rela- 
tive proportion  of  carbon  to  nitrogen  in  either  of  these  compounds  alone, 
is,  by  no  means,  the  proportion  required  in  the  diet  of  man.  Thus,  in 
albumen,  the  proportion  of  carbon  to  nitrogen  is  only  as  3  *5  to  1.  If, 
therefore,  a  man  took  into  his  body,  as  food,  sufficient  albumen  to  supply 
him  with  the  needful  amount  of  carbon,  he  would  receive  more  than  four 
times  as  much  nitrogen  as  he  wanted;  and  if  he  took  only  sufficient  to 
supply  him  with  nitrogen,  he  would  be  starved  for  want  of  carbon.  It  is 
plain,  therefore,  that  he  should  take  with  the  albuminous  part  of  his 
food,  which  contains  so  large  a  relative  amount  of  nitrogen  in  proportion 
to  the  carbon  he  needs,  substances  in  which  the  nitrogen  exists  in  much 
smaller  quantities  relatively  to  the  carbon. 

It  is  therefore  evident  that  the  diet  must  consist  of  several  substances, 
not  of  one  alone,  and  we  must  therefore  turn  to  the  available  food-stuffs. 
For  the  sake  of  convenience  they  may  be  classified  as  follows: 

A.  ORGANIC. 

I.  Nitrogenous,  consisting  of  Proteids,  e.g.  albumen,  casein,  syn- 

tonin,  gluten,  legumin  and  their  allies;  and  Gelatins,  which  in- 
clude gelatin,  elastin,  and  chondrin.  All  of  these  contain  car- 
bon, hydrogen,  oxygen,  and  nitrogen,  and  some  in  addition, 
phosphorus  and  sulphur. 

II.  Non-Nitrogenous,  comprising: 

(1.)  Amyloid  or  saccharine  bodies,  chemically  known  as  carbo- 
hydrates, since  they  contain  carbon,  hydrogen,  and  oxygen,  with 
the  last  two  elements  in  the  proportion  to  form  water,  i.e., 
H20.  To  this  class  belong  starch  and  sugar. 

(2.)  Oils  and  fats. — These  contain  carbon,  hydrogen,  and  oxy- 
gen; but  the  oxygen  is  less  in  amount  than  in  the  amyloids  and 
saccharine  bodies. 

B.  IXORGAXIC. 

I.  Mineral  and  saline  matter. 

II.  Water. 


214  HAND-BOOK    OF    PHYSIOLOGY. 

To  supply  the  loss  of  nitrogen  and  carbon,  it  is  found  by  experience 
that  it  is  necessary  to  combine  substances  which  contain  a  large  amount 
of  nitrogen  with  others  in  which  carbon  is  in  considerable  amount;  and 
although,  without  doubt,  if  it  were  possible  to  relish  and  digest  one  or 
other  of  the  above-mentioned  proteids  when  combined  with  a  due  quantity 
of  an  amyloid  to  supply  the  carbon,  such  a  diet,  together  with  salt  and 
water,  ought  to  support  life;  yet  we  find  that  for  the  purposes  of  ordinary 
life  this  system  does  not  answer,  and  instead  of  confining  our  nitrogenous 
foods  to  one  variety  of  substance  we  obtain  it  in  a  large  number  of  allied 
substances,  for  example,  in  flesh,  of  bird,  beast,  or  fish;  in  eggs;  in  milk; 
and  in  vegetables.  Arid,  again,  we  are  not  content  with  one  kind  of  ma- 
terial to  supply  the  carbon  necessary  for  maintaining  life,  but  seek  more, 
in  bread,  in  fats,  in  vegetables,  in  fruits.  Again,  the  fluid  diet  is  seldom 
supplied  in  the  form  of  pure  water,  but  in  beer,  in  wines,  in  tea  and  cof- 
fee, as  well  as  in  fruits  and  succulent  vegetables. 

Man  requires  that  his  food  should  be  cooked.  Very  few  organic  sub- 
stances can  be  properly  digested  without  previous  exposure  to  heat  and 
to  other  manipulations  which  constitute  the  process  of  cooking.  It  will 
be  well,  therefore,  to  consider  the  composition  of  the  various  substances 
employed  as  food,  and  then  to  consider  how  they  are  affected  by  cooking. 

I 

A.  FOODS  CONTAINING  PRINCIPALLY  NITROGENOUS  BODIES. 

I. — Flesh  of  Animals,  especially  of  the  ox  (beef,  veal),  sheep  (mutton, 
lamb),  pig  (pork,  bacon,  ham). 

Of  these,  beef  is  richest  in  nitrogenous  matters,  containing  about  20 
per  cent.,  whereas  mutton  contains  about  18  per  cent.,  veal,  16*5,  and 
pork,  10;  the  flesh  is  also  firmer,  more  satisfying,  and  is  supposed  to  be 
more  strengthening  than  mutton,  whereas  the  latter  is  more  digestible. 
The  flesh  of  young  animals,  such  as  lamb  and  veal,  is  less  digestible  and 
less  nutritious.  Pork  is  comparatively  indigestible,  and  contains  a  large 
amount  of  fat. 

Flesh  contains: — (1)  Nitrogenous  bodies:  myosin,  serum-albumin,  gela- 
tin (from  the  interstitial  fibrous  connective  tissue);  elastin  (from  the  elastic 
tissue),  as  well  as  hcemoglobin.  (2)  Fatty  matters,  including  lecithin  and 
cholesterin.  (3)  Extractive  matters,  some  of  which  are  agreeable  to  the 
palate,  e.g.,  osmazome,  and  others  which  are  weakly  stimulating,  e.g., 
kreatin.  Besides,  there  are  sarcolactic  and  inositic  acids,  taurin,  xanthin, 
and  others.  (4)  Salts,  chiefly  of  potassium,  calcium,  and  magnesium. 
(5)  Water,  the  amount  of  which  varies  from  15  per  cent,  in  dried  bacon 
to  39  in  pork,  51  to  53  in  fat  beef  and  mutton,  to  72  per  cent,  in  lean 
beef  and  mutton.  (6)  A  certain  amount  of  carbo-hydrate  material  is 
found  in  the  flesh  of  young  animals,  in  the  form  of  inosite,  dextrin,  grape 
sugar,  and  (in  young  animals)  glycogen. 


FOOD.  215 

Table  of  Per-centage  Composition  of  Beef,  Mutton,  Pork,  and  Veal. — 

(Letheby.) 

Water.  Albumen.      Fat.       Salts. 
Beef.— Lean  .  72        19-3          3-6        5.1 


Fat     . 
Mutton.  — Lean 

Fat 

Veal       . 
Pork.— Fat 


51  14-8  29-8  4-4 

72  18.3  4.9  4.8 

53  12-4  31-1  3'5 

63  16-5  15-8  4-7 

39  9.8  48-9  2 '3 


Together  with  the  flesh  of  the  above-mentioned  animals,  that  of  the 
deer,  hare,  rabbit,  and  birds,  constituting  venison,  game  and  poultry, 
should  be  added  as  taking  part  in  the  supply  of  nitrogenous  substances, 
and  ahofish — salmon,  eels,  etc.,  and.  shell- fish,  e.g.,  lobster,  crab,  mussels, 
oysters,  shrimps,  scollop,  cockles,  etc. 

Table  of  Per-centage  Composition  of  Poultry  and  Fish. — (Letheby.) 

Water.  Albumen.      Fats.      Salts. 
Poultry 74          21  3 -8         1-2 

(Singularly  devoid  of  fat,  and  so  generally  eaten  with  bacon  or  pork.) 

White  Fish    .         .  .  .78  18 -1        2-9  1* 

Salmon  .         .  .  .77  16.1         5 -5  1-4 

Eels  (very  rich  in  fat)  .  .75  9-9  13 -8  1-3 

Oysters  .         .    '  .  .75-74  11 '72      2-42  2.73 

Even  now  the  list  of  fleshy  foods  is  not  complete,  as  nearly  all  animals 
have  been  occasionally  eaten,  and  we  may  presume  that  the  average  com- 
position of  all  is  nearly  the  same. 

II.  MM — Is  intended  as  the  entire  food  of  young  animals,  and  as 
such  contains,  when  pure,  all  the  elements  of  a  typical  diet.  (1)  Albu- 
minous substances  in  the  form  of  casein  and,  in  small  amount,  of  serum- 
albumin.  (2)  Fats  in  the  cream.  (3)  Carbo-hydrates  in  the  form  of 
lactose  or  milk  sugar.  (4)  Salts,  chiefly  calcium  phosphate;  and  (5) 
"Water.  From  it  we  obtain  (a)  cheese,  which  is  the  casein  precipitated 
with  more  or  less  fat  according  as  the  cheese  is  made  of  skim  milk  (skim 
cheese),  of  fresh  milk  with  its  cream  (Cheddar  and  Cheshire),  or  of  fresh 
milk  plus  cream  (Stilton  and  double  Gloucester).  The  precipitated  casein 
is  allowed  to  ripen,  by  which  process  some  of  the  albumen  is  split  up  with 
formation  of  fat.  (/?)  Cream,  which  consists  of  the  fatty  globules  in- 
cased in  casein,  and  which  being  of  low  specific  gravity  float  to  the  surface. 
(y)  fitter,  or  the  fatty  matter  deprived  of  its  casein  envelope  by  the  process 
of  churning.  (6)  Buttermilk,  or  the  fluid  obtained  from  cream  after 


216 


HAND-BOOK    OF    PHYSIOLOGY. 


batter  has  been  formed;  very  rich  therefore  in  nitrogen,  (f)  Wliey,  or 
the  fluid  which  remains  after  the  precipitation  of  casein;  this  contains 
sugar,  salt,  and  a  small  quantity  of  albumen. 

Table  of  Composition  of  Milk,  Buttermilk,  Cream,  and  Cheese.  —  (Lethe- 

by  and  Pay  en.) 


Fats'       Lactose'     Salts'  Water' 


Milk  (Cow) 
Buttermilk 
Cream 

Cheese. — Skim   . 
Cheddar 


4-1 
4-1 

2-7 
44-8 
28-4 


26-7 


5.2 
6-4 

2-8 


-8  86 

-8  88 

1-8  66 

4-9  44 

4.5  36 
Non-nitrogenous 
matter  and  loss. 


6-3 
31-1 


"    Neufchatel  (fresh)  8-        40-71       36'58         -51       36.58 

III.  Eggs.  —  The  yelk  and  albumen  of  eggs  are  in  the  same  relation  as 
food  for  the  embryoes  of  oviparous  animals  that  milk  is  to  the  young  of 
mammalia,  and  afford  another  example  of  the  natural  admixture  of  the 
various  alimentary  principles. 

Table  of  the  Per-centage  Composition  of  Fozvls'  Eggs. 


White 
Yelk 


Nitrogenous 
substances. 

.     20-4 
16 


Fats. 


30-7 


Salts.      Water. 


1-6 
1-3 


78 
52 


IV.  Leguminous  fruits  are  used  by  vegetarians,  as  the  chief  source  of 
the  nitrogen  of  the  food.  Those  chiefly  used  are  peas,  beans,  lentils,  etc., 
they  contain  a  nitrogenous  substance  called  legumin,  allied  to  albumen. 
They  contain  about  25  '30  per  cent,  of  this  nitrogenous  body,  and  twice  as 
much  nitrogen  as  wheat. 

B.    SUBSTANCES  SUPPLYING  PRINCIPALLY  CARBOHYDRATE  BODIES. 

a.  Bread,  made  from  the  ground  grain  obtained  from  various  so-called 
cereals,  viz.,  wheat,  rye,  maize,  barley,  rice,  oats,  etc.,  is  the  direct  form 
in  which  the  carbohydrate  is  supplied  in  an  ordinary  diet.  Flour,  how- 
ever, besides  the  starch,  contains  gluten,  a  nitrogenous  body,  and  a  small 
amount  of  fat. 


Table  of  Per-centage  Composition  of  Bread  and  Flour. 


Bread 
Flour 


Nitrogenous    Carbo- 
matters.     hydrates. 

.        8-1  51- 

10.8          70-85 


Fats.       Salts.    Water. 


2.3 

1.7 


37 
15 


FOOD.  217 

Various  articles  of  course  are  made  from  flour,  e.g.,  macaroni,  biscuits, 
etc.,  besides  bread. 

/?.    Vegetables,  especially  potatoes. 

y.  Fruits  contain  sugar,  and  organic  acids,  tartaric,  malic,  citric,  and 
others. 

C.  SUBSTANCES  SUPPLYING  PRINCIPALLY  FATTY  BODIES. 
The  chief  are  butter,  lard  (pig's  fat),  suet  (beef  and  mutton  fat). 

D.  SUBSTANCES  SUPPLYING  THE  SALTS  OF  THE  FOOD. 

Nearly  all  the  foregoing  substances  in  A,  B,  and  C,  contain  a  greater  or 
less  amount  of  the  salts  required  in  food;  but  green  vegetables  and  fruit 
supply  certain  salts,  without  which  the  normal  health  of  the  body  is  not 
maintained. 

E.  LIQUID  FOODS. 

"Water  is  consumed  alone,  or  together  with  certain  other  substances 
used  to  flavor  it,  e.g.,  tea,  coffee,  etc.  Tea  in  moderation  is  a  stimulant, 
and  contains  an  aromatic  oil  to  which  it  owes  its  peculiar  aroma,  an  astrin- 
gent of  the  nature  of  tannin,  and  an  alkaloid,  theine.  The  composition 
of  coffee  is  very  nearly  similar  to  that  of  tea.  Cocoa,  in  addition  to 
similar  substances  contained  in  tea  and  coffee,  contains  fat,  albuminous 
matter,  and  starch,  and  must  be  looked  upon  more  as  a  food. 

Beer,  in  various  forms,  is  an  infusion  of  malt  (barley  which  has 
sprouted,  and  in  which  the  starch  is  converted  in  great  part  into  sugar), 
boiled  with  hops  and  allowed  to  ferment.  Beer  contains  from  1  '2  to  8  '8 
per  cent,  of  alcohol. 

Cider  and  Perry,  the  fermented  juice  of  the  apple  and  pear. 

Wine,  the  fermented  juice  of  the  grape,  contains  from  6  or  7  (Ehine 
wines,  and  white  and  red  Bordeaux)  to  24 — 25  (ports  and  sherries)  per 
cent,  of  alcohol. 

Spirits,  obtained  from  the  distillation  of  fermented  liquors.  They 
contain  upward  of  40 — 70  per  cent,  of  absolute  alcohol. 

Effects  c  f  cooking  upon  Food. — In  general  terms  this  may  be 
said  to  make  food  more  easily  digestible,  arid  this  includes  two  other 
alterations,  food  is  made  more  agreeable  to  the  palate  and  also  more  pleas- 
ing to  the  eye.  Cooking  consists  in  exposing  the  food  to  various  degrees 
of  heat,  either  to  the  direct  heat  of  the  fire,  as  in  roasting,  or  to  the  in- 
direct heat  of  the  fire,  as  in  broiling,  baking,  or  frying,  or  to  hot  water, 
as  in  boiling  or  stewing.  The  effect  of  heat  upon  flesh  is  to  coagulate  the 
albumen  and  coloring  matter,  to  solidify  fibrin,  and  to  gelatinize  tendons 


218  HAND-BOOK    OF    PHYSIOLOGY. 

and  fibrous  connective  tissue.  Previous  beating  or  bruising  (as  with 
steaks  and  chops,  or  keeping  (as  in  the  case  of  game),  renders  the  meat 
more  tender.  Prolonged  exposure  to  heat  also  develops  on  the  surface 
certain  empyreumatic  bodies,  which  are  agreeable  both  to  the  taste  and 
smell.  By  placing  meat  into  hot  water,  the  external  coating  of  albumen 
is  coagulated,  and  very  little,  if  any,  of  the  constituents  of  the  meat  are 
lost  afterward  if  boiling  be  prolonged,  but  if  the  constituents  of  the 
meat  are  to  be  extracted,  it  should  be  exposed  to  prolonged  simmering  at 
a  much  lower  temperature,  and  the  "broth"  will  then  contain  the  gelatin 
and  extractive  matters  of  the  meat,  as  well  as  a  certain  amount  of  albu- 
men. The  addition  of  salt  will  help  to  extract  the  myosin. 

The  effect  of  boiling  upon  an  egg  coagulates  the  albumen,  and  helps 
in  rendering  the  article  of  food  more  suitable  for  adult  dietary.  Upon 
milk,  the  eifect  of  heat  is  to  produce  a  scum  composed  of  serum-albumin 
and  a  little  casein  (the  greater  part  of  the  casein  being  uncoagulated)  with 
some  fat.  Upon  vegetables,  the  cooking  produces  the  necessary  effect  of 
rendering  them  softer,  so  that  they  can  be  more  readily  broken  up  in  the 
mouth;  it  also  causes  the  starch  to  swell  up  and  burst,  and  so  aids  the 
digestive  fluids  to  penetrate  into  their  substance.  The  albuminous  mat- 
ters are  coagulated,  and  the  gummy,  saccharine  and  saline  matters  are 
remove'd.  The  conversion  of  flour  into  bread  is  effected  by  mixing  it  with 
water,  a  little  salt  and  a  certain  amount  of  yeast,  which  consists  of  the 
cells  of  an  organized  ferment  (Torula  cerevisice).  By  the  growth  of  this 
plant,  which  lives  upon  the  sugar  produced  from  the  starch  of  the  flour, 
carbonic  acid  gas  and  a  small  amount  of  alcohol  are  formed.  It  is  by 
means  of  the  former  that  the  dough  rises.  Another  method  consists  in 
mixing  the  flour  with  water  containing  a  large  quantity  of  the  gas  in  so- 
lution. 

By  the  action  of  heat  during  baking  the  dough  continues  to  expand, 
and  the  gluten  being  coagulated,  the  bread  sets  as  a  permanently  vesicu- 
lated  mass. 

I.— EFFECTS  OF  AN  INSUFFICIENT  DIET. 

Hunger  and  Thirst. — The  sensation  of  hunger  is  manifested  in 
consequence  of  deficiency  of  food  in  the  system.  The  mind  refers  the 
sensation  to  the  stomach;  yet  since  the  sensation  is  relieved  by  the  intro- 
duction of  food  either  into  the  stomach  itself,  or  into  the  blood  through 
other  channels  than  the  stomach,  it  would  appear  riot  to  depend  on  the 
state  of  the  stomach  alone.  This  view  is  confirmed  by  the  fact,  that  the 
division  of  both  pneumogastric  nerves,  which  are  the  principal  channels 
by  which  the  brain  is  cognizant  of  the  condition  of  the  stomach,  does  not 
appear  to  allay  the  sensations  of  hunger.  But  that  the  stomach  has 
some  share  in  this  sensation  is  proved  by  the  relief  afforded,  though  only 


FOOD. 


219 


temporarily,  by  the  introduction  of  even  non-alimentary  substances  into 
this  organ.  It  may,  therefore,  be  said  that  the  sensation  of  hunger  is 
caused  both  by  a  want  in  the  system  generally,  and  also  by  the  condition 
of  the  stomach  itself,  by  which  condition,  of  course,  its  own  nerves  are 
more  directly  affected. 

The  sensation  of  thirst,  indicating  the  want  of  fluid,  is  referred  to  the 
fauces,  although,  as  in  hunger,  this  is,  in  great  part,  only  the  local  decla- 
ration of  a  general  condition.  For  thirst  is  relieved  for  only  a  very  short 
time  by  moistening  the  dry  fauces;  but  may  be  relieved  completely  by  the 
introduction  of  liquids  into  the  blood,  either  through  the  stomach,  or  by 
injections  into  the  blood-vessels,  or  by  absorption  from  the  surface  of  the 
skin  or  the  intestines.  The  sensation  of  thirst  is  perceived  most  naturally 
whenever  there  is  a  disproportionately  small  quantity  of  water  in  the 
blood:  as  well,  therefore,  when  water  has  been  abstracted  from  the  blood, 
as  when  saline  or  any  solid  matters  have  been  abundantly  added  to'  it. 
And  the  cases  of  hunger  and  thirst  are  not  the  only  ones  in  which  the 
mind  derives,  from  certain  organs,  a  peculiar  predominant  sensation  of 
some  condition  affecting  the  whole  body.  Thus,  the  sensation  of  the 
"necessity  of  breathing/'  is  referred  especially  to  the  air-passages;  but, 
as  Volkmann's  experiments  show,  it  depends  on  the  condition  of  the 
blood  which  circulates  everywhere,  and  is  felt  even  after  the  lungs  of 
animals  are  removed;  for  they  continue,  even  then,  to  gasp  and  manifest 
the  sensation  of  want  of  breath. 

Starvation. — The  effects  of  total  deprivation  of  food  have  been  made 
the  subject  of  experiments  on  the  lower  animals,  and  have  been  but  too 
frequently  illustrated  in  man.  (1)  One  of  the  most  notable  effects  of 
starvation,  as  might  be  expected,  is  loss  of  weight;  the  loss  being  greatest 
at  first,  as  a  rule,  but  afterward  not  varying  very  much,  day  by  day,  until 
death  ensues.  Chossat  found  that  the  ultimate  proportional  loss  was,  in 
different  animals  experimented  on,  almost  exactly  the  same;  death 
occurring  when  the  body  had  lost  two-fifths  (forty  per  cent.)  of  its  original 
weight.  Different  parts  of  the  body  lose  weight  in  very  different  propor- 
tions. The  following  results  are  taken,  in  round  numbers,  from  the  table 
given  by  M.  Chossat: — 


Fat 

Blood    . 

Spleen  . 

Pancreas 

Liver     . 

Heart    . 

Intestines 

Muscles  of  locomotion 

Stomach 

Pharynx,  ((Esophagus) 

Skin 


loses  93  per  cent. 
.  75  " 
.  71 
.  64 
.  52 
.  44 
.  42 
.  42 
.  39 
.  34 
33 


220  HAND-BOOK    OF    PHYSIOLOGY. 


Kidneys 

Kespiratory  apparatus 

Bones    , 

Eyes      . 

Nervous  system 


loses  31  per  cent. 
.     22       " 
.     16       ie 
.     10 

2       "  (nearly). 


(2. )  The  effect  of  starvation  on  the  temperature  of  the  various  animals 
experimented  on  by  Chossat  was  very  marked.  For  some  time  the  vari- 
ation in  the  daily  temperature  was  more  marked  than  its  absolute  and 
continuous  diminution,  the  daily  fluctuation  amounting  to  5°  or  6°  F. 
(3°  0.),  instead  of  1°  or  2°  F.  (-5°  to  1°  C.),  as  in  health.  But  a  short 
time  before  death,  the  temperature  fell  very  rapidly,  and  death  ensued 
when  the  loss  had  amounted  to  about  30°  F.  (16'5°C.).  It  has  been  often 
said,  and  with  truth,  although  the  statement  requires  some  qualification, 
that  death  by  starvation  is  really  death  by  cold;  for  not  only  has  it  been 
found  that  differences  of  time  with  regard  to  the  period  of  the  fatal  result 
are  attended  by  the  same  ultimate  loss  of  heat,  but  the  effect  of  the  appli- 
cation of  external  warmth  to  animals  cold  and  dying  from  starvation,  is 
more  effectual  in  reviving  them  than  the  administration  of  food.  In 
other  words,  an  animal  exhausted  by  deprivation  of  nourishment  is  unable 
so  to  digest  food  as  to  use  it  as  fuel,  and  therefore  is  dependent  for  heat 
on  its  supply  from  without.  Similar  facts  are  often  observed  in  the  treat- 
ment of  exhaustive  diseases  in  man. 

(3.)  The  symptoms  produced  by  starvation  in  the  human  subject  are 
hunger,  accompanied,  or  it  may  be  replaced  by  pain,  referred  to  the  region 
of  the  stomach;  insatiable  thirst;  sleeplessness;  general  weakness  and 
emaciation.  The  exhalations  both  from  the  lungs  and  skin  are  fetid, 
indicating  the  tendency  to  decomposition  which  belongs  to  badly- 
nourished  tissues;  and  death  occurs,  sometimes  after  the  additional  ex- 
haustion caused  by  diarrhoea,  often  with  symptoms  of  nervous  disorder, 
delirium  or  convulsions. 

(4.)  In  the  human  subject  death  commonly  occurs  within  six  to  ten 
days  after  total  deprivation  of  food.  But  this  period  may  be  considerably 
prolonged  by  taking  a  very  small  quantity  of  food,  or  even  water  only. 
The  cases  so  frequently  related  of  survival  after  many  days,  or  even  some 
weeks,  of  abstinence,  have  been  due  either  to  the  last-mentioned  circum- 
stances, or  to  others  no  less  effectual,  which  prevented  the  loss  of  heat 
and  moisture.  Cases  in  which  life  has  continued  after  total  abstinence 
from  food  and  drink  for  many  weeks,  or  months,  exist  only  in  the  imag- 
ination of  the  vulgar. 

(5. )  The  appearances  presented  after  death  from  starvation  are  those  of 
general  wasting  and  bloodlessness,  the  latter  condition  being  least  noticeable 
in  the  brain.  The  stomach  and  intestines  are  empty  and  contracted,  and 
the  walls  of  the  latter  appear  remarkably  thinned  and  almost  transparent. 
The  various  secretions  are  scanty  or  absent,  with  the  exception  of  the 


FOOD.  221 

bile,  which,  somewhat  concentrated,  usually  fills  the  gall-bladder.     All 
parts  of  the  body  readily  decompose. 

II. — EFFECTS  OF  IMPROPER  DIET. 

Experiments  on  Feeding. — Experiments  illustrating  the  ill  effects 
produced  by  feeding  animals  upon  one  or  two  alimentary  substances  only 
have  been  often  performed. 

Dogs  were  fed  exclusively  on  sugar  and  distilled  water.  During  the 
first  seven  or  eight  days  they  were  brisk  and  active,  and  took  their  food 
and  drink  as  usual;  but  in  the  course  of  the  second  week,  they  began  to 
get  thin,  although  their  appetite  continued  good,  and  they  took  daily 
between  six  and  eight  ounces  of  sugar.  The  emaciation  increased  during 
the  third  week,  and  they  became  feeble,  and  lost  their  activity  and  appe- 
tite. At  the  same  time  an  ulcer  formed  on  each  cornea,  followed  by  an 
escape  of  the  humors  of  the  eye:  this  took  place  in  repeated  experiments. 
The  animals  still  continued  to  eat  three  or  four  ounces  of  sugar  daily; 
but  became  at  length  so  feeble  as  to  be  incapable  of  motion,  and  died  on 
a  day  varying  from  the  thirty-first  to  the  thirty-fourth.  On  dissection, 
their  bodies  presented  all  the  appearances  produced  by  death  from  starva- 
tion; indeed,  dogs  will  live  almost  the  same  length  of  time  without  any 
food  at  all. 

When  dogs  were  fed  exclusively  on  gum,  results  almost  similar  to  the 
above  ensued.  When  they  were  kept  on  olive-oil  and  water,  all  the  phe- 
nomena produced  were  the  same,  except  that  no  ulceration  of  the  cornea 
took  place;  the  effects  were  also  the  same  with  butter.  The  experiments  of 
Chossat  and  Letellier  prove  the  same;  and  in  men,  the  same  is  shown  by 
the  various  diseases  to  which  those  who  consume  but  little  nitrogenous 
food  are  liable,  and  especially  by  the  affection  of  the  cornea  which  is 
observed  in  Hindus  feeding  almost  exclusively  on  rice.  But  it  is  not  only 
the  non-nitrogenous  substances,  which,  taken  alone,  are  insufficient  for 
the  maintenance  of  health.  The  experiments  of  the  Academies  of  France 
and  Amsterdam  were  equally  conclusive  that  gelatin  alone  soon  ceases  to 
be  nutritive. 

Savory's  observations  on  food  confirm  and  extend  the  results  obtained 
by  Magendie,  Chossat,  and  others.  They  show  that  animals  fed  exclu- 
sively on  non-nitrogenous  diet  speedily  emaciate  and  die,  as  if  from  starv- 
ation; that  life  is  much  more  prolonged  in  those  fed  with  nitrogenous 
than  by  those  with  non-nitrogenous  food;  and  that  animal  heat  is  main- 
tained as  well  by  the  former  as  by  the  latter — a  fact  which  proves,  if 
proof  were  wanting — that  nitrogenous  elements  of  food,  as  well  as  non- 
nitrogenous,  may  be  regarded  as  calorifacient. 


222  HAND-BOOK    OF    PHYSIOLOGY. 


III. — EFFECT  OF  TOO  MUCH  FOOD. 

Sometimes  the  excess  of  food  is  so  great  that  it  passes  through  the  ali- 
mentary canal,  and  is  at  once  got  rid  of  by  increased  peristaltic  action  of 
the  intestines.  In  other  cases,  the  unabsorbed  portions  undergo  putre- 
factive changes  in  the  intestines,  which  are  accompanied  by  the  produc- 
tion of  gases,  such  as  carbonic  acid,  carburetted  and  sulphuretted  hydro- 
gen; a  distended  condition  of  the  bowels,  accompanied  by  symptoms  of 
indigestion,  is  the  result.  An  excess  of  the  substances  required  as  food  may, 
however,  undergo  absorption.  It  is  a  well-known  fact  that  numbers  of 
people  habitually  eat  too  much;  especially  of  nitrogenous  food.  Dogs 
can  digest  an  immense  amount  of  meat  if  fed  often,  and  the  amount  of 
meat  taken  by  some  men  would  supply  not  only  tihe  nitrogen,  but  the 
carbon  which  is  requisite  for  an  ordinary  natural  diet.  A  method  of  get- 
ting rid  of  an  excess  of  nitrogen  is  provided  by  the  digestive  processes  in 
the  duodenum,  to  be  presently  described,  whereby  the  excess  of  the  albu- 
minous food  is  capable  of  being  changed  before  absorption  into  nitroge- 
nous crystalline  matters,  easily  converted  by  the  liver  into  urea,  and  so  easily 
excreted  by  the  kidneys,  affording  one  variety  of  what  is  called  luxus 
consumption;  but  after  a  time  the  organs,  especially  the  liver,  will  yield 
to  the  strain  of  the  over- work,  and  will  not  reduce  the  excess  of  nitroge- 
nous material  into  urea,  but  into  other  less  oxidized  products,  such  as  uric 
acid;  and  general  plethora  and  gout  may  be  the  result.  This  state  of 
things,  however,  is  delayed  for  a  long  time,  if  not  altogether  obviated, 
when  large  meat-eaters  take  a  considerable  amount  of  exercise. 

Excess  of  carbohydrate  food  produces  an  accumulation  of  fat,  which 
may  not  only  be  an  inconvenience  by  causing  obesity,  but  may  interfere 
with  the  proper  nutrition  of  muscles,  causing  a  feebleness  of  the  action 
of  the  heart,  and  other  troubles.  The  accumulation  of  fat  is  due  to  the 
excess  of  carbohydrate  being  stored  up  by  the  protoplasm  in  the  form  of 
fat.  Starches  when  taken  in  great  excess  are  almost  certain  to  give  rise  in 
addition  to  dyspepsia,  with  acidity  and  flatulence.  There  is  a  limit  to 
the  absorption  of  starch  and  of  fat,  as,  if  taken  beyond  a  certain  amount, 
they  appear  unchanged  in  the  faeces. 

Requisites  of  a  Normal  Diet. — It  will  have  been  understood  that 
it  is  necessary  that  a  normal  diet  should  be  made  up  of  various  articles, 
that  they  should  be  well  cooked,  and  should  contain  about  the  same 
amount  of  the  carbon  and  nitrogen  that  are  got  rid  of  by  the  excreta. 
Without  doubt  these  desiderata  may  be  satisfied  in  numerous  ways,  and 
it  would  be  simply  absurd  to  believe  that  the  diet  of  every  adult  should 
be  exactly  similar.  The  age,  sex,  strength,  and  circumstances  of  each 
individual  should  ultimately  determine  his  diet.  A  dinner  of  bread  and 
hard  cheese  with  an  onion  contain  all  the  requisites  for  a  meal;  but  such 


FOOD.  223 

diet  would  be  suitable  only  for  those  possessing  strong  digestive  powers. 
It  is  a  well- known  fact  that  the  diet  of  the  continental  nations  differs 
from  that  of  our  own  country,  and  that  of  cold  from  that  of  hot  climates; 
but  the  same  principle  underlies  them  all,  viz.,  replacement  of  the  loss 
of  the  excreta  in  the  most  convenient  and  economical  way  possible. 
Without  going  into  detail  in  the  matter,  it  may  be  said  that  any  one  in 
active  work  requires  more  nitrogenous  matter  than  one  at  rest,  and  that 
children  and  women  require  less  than  adult  men. 

The  quantity  of  food  for  a  healthy  adult  man  of  average  height  and 
weight  may  be  stated  in  the  following  table: — 

Table  of  Water  and  Food  required  for  a  Healthy  Adult. — (Parkes.) 

In  laborious          Af       . 
occupation. 

Nitrogenous  substances,  e.g.,  flesh      6  to  7  oz.  av.  2 -5  oz. 

Fats 3 '5  to  4-5  oz.  1  oz. 

Carbo-hydrates     .         .         .         .  16  to  18  oz.  12  oz. 

Salts  1.2  to  1.5  oz.  .5  oz. 


26'7  to  31  oz.         16  oz. 

The  above  is  the  dry  food;  but  as  this  is  nearly  always  combined  with 
50  to  60  per  cent,  of  water,  these  numbers  should  be  doubled,  and  they 
would  then  be  52  to  60  oz.,  and  32  oz.  of  so  called  solid  food,  and  to  this 
should  be  added  50  to  80  oz.  of  fluid. 

Full  diet  scale  for  an  adult  male  in  hospital   (St.  Bartholomew's 

Hospital}. 

Breakfast. — 1  pint  of  tea  (with  milk  and  sugar),  bread  and  butter. 

Dinner. — -J-lb.  of  cooked  meat,  |lb.  potatoes,  bread  and  beer. 

Tea. — 1  pint  of  tea,  bread  and  butter. 

Supper. — Bread  and  butter,  beer. 

Daily  allowance  to  each  patient. — 2  pints  of  tea,  with  milk  and  sugar; 
14  oz.  bread;  \  Ib.  of  cooked  meat:  £lb.  potatoes:  2  pints  of  beer,  1  oz. 
butter.  31  oz"  solid,  and  4  pints  (80  oz.),  liquid. 


CHAPTEK  VIII. 

DIGESTION. 

THE  object  of  digestion  is  to  prepare  the  food  to  supply  the  waste  of 
the  tissues,  which  we  have  seen  is  its  proper  function  in  the  economy. 
Few  of  the  articles  of  diet  are  taken  in  the  exact  condition  in  which  it  is 
possible  for  them  to  be  absorbed  into  the  system  by  the  blood-vessels  and 
lymphatics,  without  which  absorption  they  would  be  useless  for  the  pur- 
poses they  have  to  fulfil;  almost  the  whole  of  the  food  undergoes  various 
changes  before  it  is  fit  for  absorption.  Having  been  received  into  the 
mouth,  it  is  subjected  to  the  action  of  the  teeth  and  tongue,  and  is  mixed 
with  the  first  of  the  digestive  juices — the  saliva.  It  is  then  swallowed, 
and,  passing  through  the  pharynx  and  oesophagus  into  the  stomach,  is 
subjected  to  the  action  of  the  gastric  juice.  Thence  it  passes  into  the 
intestines,  where  it  meets  with  the  bile,  the  pancreatic  juice  and  the  in- 
testinal juices,  all  of  which  exercise  an  influence  upon  that  portion  of  the 
food  not  absorbed  from  the  stomach.  By  this  time  most  of  the  food  is 
'capable  of  absorption,  and  the  residue  of  undigested  matter  leaves  the 
body  in  the  form  of  faeces  by  the  anus. 

The  course  of  the  food  through  the  alimentary  canal  of  man  will  be 
readily  seen  from  the  accompanying  diagram  (Fig.  165). 

The  Mouth  is  the  cavity  contained  between  the  jaws  and  inclosed 
by  the  cheeks  laterally,  and  by  the  lips  in  front;  behind  it  opens  into  the 
pharynx  by  the  fauces,  and  is  separated  from  the  nasal  cavity  by  the  hard 
palate  in  front,  and  the  soft  palate  behind,  which  form  its  roof.  The 
tongue  forms  the  lower  part  or  floor.  In  the  jaws  are  contained  the 
teeth;  and  when  the  mouth  is  shut  these  form  its  anterior  and  lateral 
boundaries.  The  whole  of  the  mouth  is  lined  with  mucous  membrane, 
covered  by  stratified  squamous  epithelium,  which  is  continuous  in  front 
along  the  lips  with  the  epithelium  of  the  skin,  and  posteriorly  with  that 
of  the  pharynx.  The  mucous  membrane  is  provided  with  numerous 
glands  (small  tubular),  called  mucous  glands,  and  into  it  open  the  ducts 
of  the  salivary  glands,  three  chief  glands  on  each  side.  The  tongue  is 
not  only  a  prehensile  organ,  but  is  also  the  chief  seat  of  the  sense  of  taste. 

"We  shall  now  consider,  in  detail,  the  process  of  digestion,  as  it  takes 
place  in  each  stage  of  this  journey  of  the  food  through  the  alimentary 
canal. 

Mastication. — The  act  of  chewing  or  mastication  is  performed  by 


DIGESTION.  225 

the  biting  and  grinding  movement  of  the  lower  range  of  teeth  against  the 
upper.  The  simultaneous  movements  of  the  tongue  am^heeks  assist  partly 
by  crushing  the  softer  portions  of  the  food  against  the  hard  palate,  gums, 
etc.,  and  thus 'supplementing  the  action  of  the  teeth,  and  partly  by  re- 
turning the  morsels  of  food  to  the  action  of  the  teeth,  again  and  again, 


_     FIG.  165.— Diagram  of  the  Alimentary  Canal.    The  small  intestine  of  man  is  from  about  3  to  4 
tunes  as  long  as  the  large  intestine. 

as  they  are  squeezed  out  from  between  them,  until  they  have  been  suffi- 
ciently chewed. 

The  simple  up  and  down,  or  biting  movements  of  the  lower  jaw,  are 
performed  by  the  temporal,  masseter,  and  internal  pterygoid  muscles,  the 
action  of  which  in  closing  the  jaws  alternates  with  that  of  the  digastric 
and  other  muscles  passing  from  the  os  hyoides  to  the  lower  jaw,  which 
open  them.  The  grinding  or  side  to  side  movements  of  the  lower  jaw 
are  performed  mainly  by  the  external  pterygoid  muscles,  the  muscle  of 
one  side  acting  alternately  with  the  other.  When  both  external  ptery- 
VOL.  I.— 15. 


226  HAND-BOOK    OF    PHYSIOLOGY. 

golds  act  together,  the  lower  jaw  is  pulled  directly  forward,  so  that  the 
lower  incisor  teeth  ^e  brought  in  front  of  the  level  of  the  upper. 

Temporo-maxillary  Fibro-cartilage.— The  function  of  the  inter- 
articular  fibro-cartilage  of  the  temporo-maxillary  joint  in  mastication 
may  be  here  mentioned.  (1)  As  an  elastic  pad,  it  serves  well  to  distrib- 
ute the  pressure  caused  by  the  exceedingly  powerful  action  of  the  masti- 
catory muscles.  (2)  It  also  serves  as  a  joint-surface  or  socket  for  the 
condyle  of  the  lower  jaw,  when  the  latter  has  been  partially  drawn  for- 
ward out  of  the  glenoid  cavity  of  the  temporal  bone  by  the  external  ptery- 
goid  muscle,  some  of  the  fibres  of  the  latter  being  attached  to  its  front 
.surface,  and  consequently  drawing  it  forward  with  the  condyle  which 
moves  on  it. 

Nerve-mechanism  of  Mastication. — As  in  the  case  of  so  many 
other  actions,  that  of  mastication  is  partly  voluntary  and  partly  reflex 
and  involuntary.  The  consideration  of  such  sensor  i-mot  or  actions  will 
come  hereafter  (see  Chapter  011  the  Nervous  System).  It  will  suffice  here 
to  state  that  the  nerves  chiefly  concerned  are  the  sensory  branches  of  the 
fifth  and  the  glosso-pharyngeal,  and  the  motor  branches  of  the  fifth  and 
the  ninth  (hypoglossal)  cerebral  nerves.  The  nerve-centre  through  which 
the  reflex  action  occurs,  and  by  which  the  movements  of  the  various 
muscles  are  harmonized,  is  situate  in  the  medulla  oblongata.  In  so  far 
as  mastication  is  voluntary  or  mentally  perceived,  it  becomes  so  under 
the  influence,  in  addition  to  the  medulla  oblongata,  of  the  cerebral  hemi- 
spheres. 

Insalivation. — The  act  of  mastication  is  much  assisted  by  the  saliva 
which  is  secreted  by  the  salivary  glands  in  largely  increased  amount 
during  the  process,  and  the  intimate  incorporation  of  which  with  the 
food,  as  it  is  being  chewed,  is  termed  insaUvation. 

THE  SALIVARY  GLANDS. 

The  salivary  glands  are  the  parotid,  the  sub-maxillary,  and  the  siib- 
lingual,  and  numerous  smaller  bodies  of  similar  structure,  and  with  sep- 
arate ducts,  which  are  scattered  thickly  beneath  the  mucous  membrane  of 
the  lips,  cheeks,  soft  palate,  and  root  of  the  tongue. 

Structure. — The  salivary  glands  are  usually  described  as  compound 
tubular  glands.  They  are  made  up  of  lobules.  Each  lobule  consists 
of  the  branchings  of  a  subdivision  of  the  main  duct  of  the  gland,  which 
are  generally  more  or  less  convoluted  toward  their  extremities,  and  some- 
times, according  to  some  observers,  sacculated  or  pouched.  The  convo- 
luted or  pouched  portions  form  the  alveoli,  or  proper  secreting  parts  of 
the  gland.  The  alveoli  are  composed  of  a  basement  membrane  of  flattened 
•cells  joined  together  by  processes  to  produce  a  fenestrated  membrane,  the 
spaces  of  which  are  occupied  by  a  homogeneous  ground-substance.  With- 
in, upon  this  membrane,  which  forms  the  tube,  the  nucleated  salivary 


DIGESTION.  227 

secreting  cells,  of  cubical  or  columnar  form,  are  arranged  parallel  to  one 
another  surrounding  a  middle  central  canal.  The  granular  appearance 
which  is  frequently  seen  in  the  salivary  cells  is  due  to  the  very  dense  net- 
work of  fibrils  which  they  contain.  When  isolated,  the  cells  not  unfre- 
quently  are  found  to  be  branched.  Connecting  the  alveoli  into  lobules  is 
a  considerable  amount  of  fibrous  connective  tissue,  which  contains  both 
flattened  and  granular  protoplasmic  cells,  lymph  corpuscles,  and  in  some 
cases  fat  cells.  The  lobules  are  connected  to  form  larger  lobules  (lobes), 
in  a  similar  manner.  The  alveoli  pass  into  the  intralobular  ducts  by  a 
narrowed  portion  (intercalary),  lined  with  flattened  epithelium  with  elon- 
gated nuclei.  The  intercalary  ducts  pass  into  the  intralobular  ducts  by 
a  narrowed  neck,  lined  with  cubical  cells  with  small  nuclei.  The  intra- 
lobular duct  is  larger  in  size,  and  is  lined  with  large  columnar  nucleated 


-  166.—  Section  of  submaxillary  gland  of  dog.    Showing  gland-cells,  &,  and  a  duct,  a,  in  section. 


cells,  the  parts  of  which,  toward  the  lumen  of  the  tube,  presents  a  fine 
longitudinal  striation,  due  to  the  arrangement  of  the  cell  network.  It  is 
most  marked  in  the  submaxillary  gland.  The  intralobular  ducts  pass  into 
the  larger  ducts,  and  these  into  the  main  duct  of  the  gland.  As  these 
ducts  become  larger  they  acquire  an  outside  coating  of  connective  tissue, 
and  later  on  some  unstriped  muscular  fibres.  The  lining  of  the  larger 
ducts  consists  of  one  or  more  layers  of  columnar  epithelium,  containing 
an  intracellular  network  of  fibres  arranged  longitudinally. 

Varieties.  —  Certain  differences  in  the  structure  of  salivary  glands 
may  be  observed  according  as  the  glands  secrete  pure  saliva,  or  saliva 
mixed  with  mucus,  or  pure  mucus,  and  therefore  the  glands  have  been 
classified  as:  (1)  True  salivary  glands  (called  most  unfortunately  by  some 
serous  glands),  e.g.,  the  parotid  of  man  and  other  animals,  and  the  sub- 
maxillary of  the  rabbit  and  guinea-pig  (Fig.  167).  In  this  kind  the 
alveolar  lumen  is  small,  and  the  cells  lining  the  tubule  are  short,  granular 
columnar  cells,  with  nuclei  presenting  the  intranuclear  network.  During 
rest  the  cells  become  larger,  highly  granular,  with  obscured  nuclei,  and 
the  lumen  becomes  smaller.  During  activity,  and  after  stimulation  of 


228 


HAND-BOOK    OF    PHYSIOLOGY. 


the  sympathetic,  the  cells  become  smaller  and  their  contents  more  opaque; 
the  granules  first  of^all  disappearing  from  the  outer  part  of  the  cells,  and 
then  being  found  only  at  the  extreme  inner  part  and  contiguous  border  of 
the  cell.  The  nuclei  reappear,  as  does  also  the  lumen.  (2)  In  the  true 
mucus-secreting  glands,  as  the  sublingual  of  man  and  other  animals,  and 


FIG.  16? 


FIG.  168. 


FIG.  167.— From  a  section  through  a  true  salivary  gland,  a,  the  gland  alveoli,  lined  with  albu- 
minous "  salivary  cells;11  b,  intralobular  duct  cut  transversely.  (Klein  and  Noble  Smith.) 

FIG.  168. — From  a  section  through  a  mucous  gland  in  a  quiescent  state.  The  alveoli  are  lined  with 
transparent  mucous  cells,  and  outside  these  are  the  demilunes  of  Heidenhain.  The  cells  should  have 
been  represented  as  more  or  less  granular.  (Heidenhain.) 

in  the  submaxillary  of  the  dog,  the  tubes  are  larger,  contain  a  larger 
lumen,  and  also  have  larger  cells  lining  them.  The  cells  are  of  two  kinds, 
(a)  mucous  or  central  cells,  which  are  transparent  columnar  cells  with, 
nuclei  near  the  basement  membrane.  The  cell  substance  is  made  up  of  a 

fine  network,  which  in  the  resting  state 
contains  a  transparent  substance  called 
mucigen,  during  which  the  cell  does  not 
stain  well  with  logwood  (Fig.  168). 
When  the  gland  is  secreting,  mucigen 
is  converted  into  mucin,  and  the  cells 
swell  up,  appear  more  transparent,  and 
stain  deeply  in  logwood  (Fig.  109). 
During  rest,  the  cells  become  smaller 
and  more  granular  from  having  dis- 
charged their  contents,  and  the  nuclei 
appear  more  distinct,  (b)  Semilunes  of 
Heidenhain  (Fig.  168),  which  are  cre- 
scentic  masses  of  granular  parietal  cells  found  here  and  there  between  the 
basement  membrane  and  the  central  cells.  These , cells  are  small,  and 
have  a  very  dense  reticulum,  the  nuclei  are  spherical,  and  increase  in  size 
during  secretion.  In  the  mucous  gland  there  are  some  large  tubes,  lined 
with  large  transparent  central  cells,  and  have  besides  a  few  granular 
parietal  cells;  other  small  tubes  are  lined  with  small  granular  parietal 


FIG.  169.— A  part  of  a  section  through  a 
mucous  gland  after  prolonged  electrical 
stimulation.  The  alveoli  are  lined  with  small 
granular  cells.  (Lavdovski.) 


DIGESTION.  229 

cells  alone;  and  a  third  variety  are  lined  equally  with  each  kind  of  cell. 
(3)  In  the  muco-salivary  or  mixed  glands,  as  the  human  submaxillary 
gland,  part  of  the  gland  presents  the  structure  of  the  mucous  gland, 
whilst  the  remainder  has  that  of  the  salivary  glands  proper. 

Nerves  and  blood-vessels. — Nerves  of  large  size  are  found  in  the  sali- 
vary glands,  they  are  contained  in  the  connective  tissue  of  the  alveoli 
principally,  and  in  certain  glands,  especially  in  the  dog,  are  provided  with 
ganglia.  Some  nerves  have  special  endings  in  Pacinian  corpuscles,  some 
supply  the  blood-vessels,  and  others,  according  to  Pfliiger,  penetrate  the 
basement  membrane  of  the  alveoli  and  enter  the  salivary  cells. 

The  blood-vessels  form  a  dense  capillary  network  around  the  ducts  of 
the  alveoli,  lUing  carried  in  by  the  fibrous  trabeculae  between  the  alveoli, 
in  which  also  begin  the  lymphatics  by  lacunar  spaces. 

Saliva. — Saliva,  as  it  commonly  flows  from  the  mouth,  is  mixed  with 
the  secretion  of  the  mucous  glands,  and  often  with  air  bubbles,  which, 
being  retained  by  its  viscidity,  make  it  frothy.  When  obtained  from  the 
parotid  ducts,  and  free  from  mucus,  saliva  is  a  transparent  watery  fluid, 
the  specific  gravity  of  which  varies  from  1004  to  1008,  and  in  which, 
when  examined  with  the  microscope,  are  found  floating  a  number  of  min- 
ute particles,  derived  from  the  secreting  ducts  and  vesicles  of  the  glands. 
In  the  impure  or  mixed  saliva  are  found,  besides  these  particles,  numer- 
ous epithelial  scales  separated  from  the  surface  of  the  mucous  membrane 
of  the  mouth  and  tongue,  and  the  so-called  salivary  corpuscles,  discharged 
probably  from  the  mucous  glands  of  the  mouth  and  the  tonsils,  which, 
when  the  saliva  is  collected  in  a  deep  vessel,  and  left  at  rest,  subside  in 
the  form  of  a  white  opaque  matter,  leaving  the  supernatant  salivary  fluid 
transparent  and  colorless,  or  with  a  pale  bluish-grey  tint.  In  reaction, 
the  saliva,  when  first  secreted,  appears  to  be  always  alkaline.  During  fast- 
ing, the  saliva,  although  secreted  alkaline,  shortly  becomes  neutral;  and 
it  does  so  especially  when  secreted  slowly  and  allowed  to  mix  with  the 
acid  mucus  of  the  mouth,  by  which  its  alkaline  reaction  is  neutralized. 

Chemical  Composition  of  Mixed  Saliva  (Frerichs). 

Water 994-10 

Solids 5-90 

Ptyalin .1-41 

Fat 0.07 

Epithelium  and  Proteids  (including  Serum-Al- 
bumin, Globulin,  Mucin,  &c.)     .         .         .         2.13 
Salts — Potassium  Sulpho-Cyanate 

Sodium  Phosphate      .... 
Calcium  Phosphate      .... 
Magnesium  Phosphate 
Sodium  Chloride          .... 
Potassium  Chloride 


2-29 


5-90 


230  HAND-BOOK    OF    PHYSIOLOGY. 

The  presence  of  potassium  sulphocyanate  (or  tliiocyanate)  {C  N  K  S) 
in  saliva,  may  be  shown  by  the  blood-red  coloration  which  the  fluid  gives 
with  a  solution  of  ferric  chloride  (Fe2016),  and  which  is  bleached  on 
the  addition  of  a  solution  of  mercuric  chloride  (HgCla). 

Rate  of  Secretion  and  Quantity. — The  rate  at  which  saliva  is 
secreted  is  subject  to  considerable  variation.  When  the  tongue  and 
muscles  concerned  in  mastication  are  at  rest,  and  the  nerves  of  the  mouth 
are  subject  to  no  unusual  stimulus,  the  quantity  secreted  is  not  more  than 
sufficient,  with  the  mucus,  to  keep  the  mouth  moist.  During  actual 
secretion  the  flow  is  much  accelerated. 

The  quantity  secreted  in  twenty-four  hours  varies;  its  average  amount 
is  probably  from  1  to  3  pints  (1  to  2  litres).  • 

Uses  of  Saliva.— The  purposes  served  by  saliva  are  (1)  mechanical  and 
(2)  chemical.  I.  Mechanical.— (1)  It  keeps  the  mouth  in  a  due  condition 
of  moisture,  facilitating  the  movements  of  the  tongue  in  speaking,  and 
the  mastication  of  food.  (2)  It  serves  also  in  dissolving  sapid  substances, 
and  rendering  them  capable  of  exciting  the  nerves  of  taste.  But  the 
principal  mechanical  purpose  of  the  saliva  is,  (3)  that  by  mixing  with  the 
food  during  mastication,  it  makes  it  a  soft  pulpy  mass,  such  as  may  be 
easily  swallowed.  To  this  purpose  the  saliva  is  adapted  both  by  quantity 
and  quality.  For,  speaking  generally,  the  quantity  secreted  during  feed- 
ing is  in  direct  proportion  to  the  dryness  and  hardness  of  the  food.  The 
quality  of  saliva  is  equally  adapted  to  this  end.  It  is  easy  to  see  how 
much  more  readily  it  mixes  with  most  kinds  of  food  than  water  alone 
does;  and  the  saliva  from  the  parotid,  labial,  and  other  small  glands, 
being  more  aqueous  than  the  rest,  is  that  which  is  chiefly  braided  and 
mixed  with  the  food  in  mastication;  while  the  more  viscid  mucous  secre- 
tion of  the  submaxillary,  palatine,  and  tonsillitic  glands  is  spread  over 
the  surface  of  the  softened  mass,  to  enable  it  to  slide  more  easily  through 
the  fauces  and  oesophagus.  II.  Chemical. — Saliva  has  the  power  of  con- 
verting starch  into  glucose  or  grape-sugar.  When  saliva,  or  a  portion  of 
a  salivary  gland,  is  added  to  starch  paste  in  a  test-tube,  and  the  mixture 
kept  at  a  temperature  of  100°  F.  (37 -8°  C.),  the  starch  is  very  rapidly 
transformed  into  grape-sugar.  There  is  an  intermediate  stage  in  which  a 
part  or  the  whole  of  the  starch  becomes  dextrin. 

Test  for  Glucose. — In  such  an  experiment  the  presence  of  sugar  is  at 
once  discovered  by  the  application  of  Trommer's  test,  which  consists  in 
the  addition  of  a  drop  or  two  of  a  solution  of  copper  sulphate,  followed 
by  a  larger  quantity  of  caustic  potash.  When  the  liquid  is  boiled,  an 
orange-red  precipitate  of  copper  suboxide  indicates  the  presence  of  sugar; 
and  when  common  raw  starch  is  masticated  and  mingled  with  saliva,  and 
kept  with  it  at  a  temperature  of  90°  or  100°  F.  (30°— 37.8°  C.),  the 
starch-grains  are  cracked  or  eroded,  and  their  contents  are  transformed 
in  the  same  manner  as  the  starch-paste. 


DIGESTION.  231 

Saliva  from  the  parotid  is  less  viscid,  less  alkaline,  clearer,  and  more 
watery  than  that  from  the  submaxillary.  It  has,  moreover,  a  less  power- 
ful action  on  starch.  Sublingual  saliva  is  the  most  viscid,  and  contains 
more  solids  kthan  either  of  the  other  two,  but  does  not  appear  to  be  so 
powerful  in  its  action. 

The  salivary  glands  of  children  do  not  become  functionally  active  till 
the  age  of  4  to  6  months,  and  hence  the  bad  effect  of  feeding  them  before 
this  age  on  starchy  food,  corn-flour,  etc.,  which  they  are  unable  to  render 
soluble  and  capable  of  absorption. 

Action  of  Saliva  on  Starch.— This  action  is  due  to  the  presence 
in  the  saliva^  of  the  body  called  ptyalin.  It  is  a  nitrogenous  body,  and 
belongs  to  the  order  of  ferments,  which  are  bodies  whose  exact  chemical 
composition  is  unknown,  and  which  are  capable  of  producing  by  their 
presence  changes  in  other  bodies,  without  themselves  undergoing  change. 
Ptyalin  is  called  a  liydrolytic  ferment,  that  is  to  say,  it  acts  by  adding  a 
molecule  of  water  to  the  body  changed.  The  reaction  is  supposed  to  be 
as  follows: 

3  C.H1006  +  3  H,0  =  C,H,,06  +  2  (C.H,00S)  +  2  H50  =  3  O.H,,0, 

Starch       +  Water.        Glucose  Dextrin  Glucose 

But  it  is  not  unlikely  that  the  action  is  by  no  means  so  simple.  In 
the  first  place,  recent  observers  believe  that  a  molecule  of  starch  must  be 
represented  by  a  much  more  complex  formula;  next,  that  the  stages  in 
the  reaction  are  more  numerous  and  extensive;  and  thirdly,  that  the  pro- 
duct of  the  reaction  is  not  true  glucose,  but  maltose.  Maltose  is  a  sugar 
more  akin  to  cane  than  grape  sugar,  of  very  little  sweetening  power,  and 
with  less  reducing  power  over  copper  salts.  Its  formula  is  C12H22On. 

The  action  of  saliva  on  starch  is  facilitated  by:  (a)  Moderate  heat, 
about  100°  F.  (37'8°  C.).  (b)  A  slightly  alkaline  medium,  (c)  Removal 
of  the  changed  material  from  time  to  time.  Its  action  is  retarded  by:  (a) 
Cold;  a  temperature  of  32°  F.  (0°  C.)  stops  it  for  a  time,  but  does  not 
destroy  it,  whereas  a  high  temperature  above  140°  F.  (60°  C.)  destroys 
it.  (b)  Acids  or  strong  alkalies  either  delay  or  stop  the  action  altogether. 
(c)  Presence  of  too  much  of  the  changed  material.  Ptyalin,  in  that  it 
converts  starch  into  sugar,  is  an  amylolytic  ferment. 

Starch  appears  to  be  the  only  principle  of  food  upon  which  saliva  acts 
chemically:  it  has  no  apparent  influence  on  any  of  the  other  ternary  prin- 
ciples, such  as  sugar,  gum,  cellulose,  or  on  fat,  and  seems  to  be  equally 
destitute  of  power  over  albuminous  and  gelatinous  substances. 

Influence  of  the  Nervous  System.— The  secretion  of  saliva  is 
under  the  control  of  the  nervous  system.  It  is  a  reflex  action,  and  in 
ordinary  conditions  is  excited  by  the  stimulation  of  the  peripheral 
branches  of  two  nerves,  viz.,  the  gustatory  or  lingual  branch  of  the  in- 


232  HAND-BOOK    OF    PHYSIOLOGY. 

f erior  maxillary  division  of  the  fifth  nerve,  and  the  glosso-pharyngeal  part 
of  the  eighth  pair  of  nerves,  which  are  distributed  to  the  mucous  mem- 
brane of  the  tongue  and  pharynx.  The  stimulation  occurs  on  the  intro- 
duction of  sapid  substances  into  the  mouth,  and  the  secretion  is  brought 
about  in  the  following  way.  From  the  terminations  of  these  sensory 
nerves  in  the  mucous  membrane  an  impression  is  conveyed  upward  (affer- 
ent) to  the  special  nerve  centre  situated  in  the  medulla,  which  controls 
the  process,  and  by  it  is  reflected  to  certain  nerves  supplied  to  the  salivary 
glands,  which  will  be  presently  indicated.  In  other  words,  the  centre, 
stimulated  to  action  by  the  sensory  impressions  carried  to  it,  sends  out 
impulses  along  efferent  or  secretory  nerves  supplied  to  the  salivary  glands, 
which  cause  the  saliva  to  be  secreted  by  and  discharged  from  the  gland 
cells.  Other  stimuli,  however,  besides  that  of  the  food,  and  other  sensory 
nerves  besides  those  mentioned,  may  produce  reflexly  the  same  effects. 
Saliva  may  be  caused  to  flow  by  irritation  of  the  mucous  membrane  of  the 
mouth  with  mechanical,  chemical,  electrical,  or  thermal  stimuli,  also  by 
the  irritation  of  the  mucous  membrane  of  the  stomach  in  some  way,  as  in 
nausea,  which  precedes  vomiting,  when  some  of  the  peripheral  fibres  of 
the  vagi  are  irritated.  Stimulation  of  the  olfactory  nerves  by  smell  of 
food,  of  the  optic  nerves  by  the  sight  of  it,  and  of  the  auditory  nerves 
by  the  sounds  which  are  known  by  experience  to  accompany  the  prepa- 
ration of  a  meal,  may  also,  in  the  hungry,  stimulate  the  nerve  centre  to 
action.  In  addition  to  these,  as  a  secretion  of  saliva  follows  the  move- 
ment of  the  muscles  of  mastication,  it  may  be  assumed  that  this  move- 
ment stimulates  the  secreting  nerve  fibres  of  the  gland,  directly  or  re- 
flexly. From  the  fact  that  the  flow  of  saliva  may  be  increased  or  dimin- 
ished by* mental  emotions,  it  is  evident  that  impressions  from  the  cere- 
brum also  are  capable  of  stimulating  the  centre  to  action  or  of  inhibiting 
its  action. 

Secretion  may  be  excited  by  direct  stimulation  of  the  centre  in  the 
medulla. 

A.  On  the  Submaxillary  Gland. — The  submaxillary  gland  has  been 
the  gland  chiefly  employed  for  the  purpose  of  experimentally  demonstra- 
ting the  influence  of  the  nervous  system  upon  the  secretion  of  saliva,  be- 
cause of  the  comparative  facility  with  which,  with  its  blood-vessels  and 
nerves,  it  may  be  exposed  to  view  in  the  dog,  rabbit,  and  other  animals. 
The  chief  nerves  supplied  to  the  gland  are:  (1)  the  chorda  tympani  (a 
branch  given  off  from  the  facial  portio  dura  of  the  seventh  pair  of  nerves), 
in  the  canal  through  which  it  passes  in  the  temporal  bone,  in  its  passage 
from  the  interior  of  the  skull  to  the  face;  and  (2)  branches  of  the  sym- 
pathetic nerve  from  the  plexus  around  the  facial  artery  and  its  branches 
to  the  gland.  The  chorda  (Fig.  170,  ch.  t.),  after  quitting  the  temporal 
bone,  passes  downward  and  forward,  under  cover  of  the  external  pterygoid 
muscle,  and  joins  at  an  acute  angle  the  lingual  or  gustatory  nerve,  pro- 


DIGESTION.  233 

ceeds  with  it  for  a  short  distance,  and  then  passes  along  the  submaxillary 
gland  duct  (Fig.  170,  sm.  d.),  to  which  it  is  distributed,  giving  branches 
to  the  submaxillary  ganglion  (Fig.  170,  sm.  gl.),  and  sending  others  to 
terminate  in  the  superficial  muscle  of  the  tongue.  If  this  nerve  be  exposed 
and  divided  anywhere  in  its  course  from  its  exit  from  the  skull  to  the 
gland,  the  secretion,  if  the  gland  be  in  action,  is  arrested,  and  no  stimu- 
lation either  of  the  lingual  or  of  the  glosso-pharyngeal  will  produce  a  flow 
of  saliva.  But  if  the  peripheral  end  of  the  divided  nerve  be  stimulated, 
an  abundant  secretion  of  saliva  ensues,  and  the  blood  supply  is  enormously 


FIG.  170.— Diagrammatic  representation  of  the  submaxillary  gland  of  the  dog  with  its  nerves  and 
blood-vessels.  (This  is  not  intended  to  illustrate  the  exact  anatomical  relations  of  the  several  struct- 
ures.) sm.  gld.,  the  submaxillary  gland  into  the  duct  (sm.  d.),  of  which  a  cannula  has  been  tied. 
The  sublingual  gland  and  duct  are  not  shown.  n.L,  n.l'.,  the  lingual  or  gustatory  nerve;  ch.  t.,  ch.  £'., 
the  chorda  tympani  proceeding  from  the  facial  nerve,  becoming  conjoined  with  the  lingual  at  n.  I'., 
and  afterward  diverging  and  passing  to  the  gland  along  the  duct;  sm.  gl..  submaxillary  ganglion 
with  its  roots;  n.  /.,  the  lingual  nerve  proceeding  to  the  tongue;  a.  car.,  the  carotid  artery,  two 
branches  of  which,  a.  sm.  a.  and  r.  sm.  p.,  pass  to  the  anterior  and  posterior  parts  of  the  gland;  v. 
.S//1..  the  anterior  and  posterior  veins  from  the  gland  ending  in  v.  j.,  the  jugular  vein;  v.  sym.,  the  con- 
joined vagus  and  sympathetic  trunks;  gl.  cer.  s.,  the  superior-cervical  ganglion,  two  branches  of  which 
forming  a  plexus,  a./.,  over  the  facial  artery  are  distributed  (n.  sym.  sm.)  along  the  two  glandular 
arteries  to  the  anterior  and  posterior  portion  of  the  gland.  The  arrows  indicate  the  direction  taken 
by  the  nervous  impulses;  during  reflex  stimulations  of  the  gland  they  ascend  to  the  brain  by  the  lin- 
gual and  descend  by  the  chorda  tympani.  (M.  Foster.) 


increased,  the  arteries  being  dilated.  The  veins  even  pulsate,  and  the 
blood  contained  within  them  is  more  arterial  than  venous  in  character. 

When,  on  the  other  hand,  the  stimulus  is  applied  to  the  sympathetic 
filaments  (mere  division  producing  no  apparent  effect),  the  arteries  con- 
tract, and  the  blood  stream  is  in  consequence  much  diminished;  and  from 
the  veins,  when  opened,  there  escapes  only  a  sluggish  stream  of  dark 
blood.  The  saliva,  instead  of  being  abundant  and  watery,  becomes  scanty 
and  tenacious.  If  both  chorda  tympani  and  sympathetic  branches  be  di- 
vided, the  gland,  released  from  nervous  control,  secretes  continuously  and 
abundantly  (paralytic)  secretion. 

The  abundant  secretion  of  saliva,   which  follows  stimulation  of  the 


234  HAND-BOOK    OF    PHYSIOLOGY. 

chorda  tympani,  is  not  merely  the  result  of  a  filtration  of  fluid  from  the 
blood-vessels,  in  consequence  of  the  largely  increased  circulation  through 
them.  This  is  proved  by  the  fact  that,  when  the  main  duct  is  obstructed, 
the  pressure  within  may  considerably  exceed  the  blood-pressure  in  the 
arteries,  and  also  that  when  into  the  veins  of  the  animal  experimented 
upon  some  atropin  has  been  previously  injected,  stimulation  of  the 
peripheral  end  of  the  divided  chorda  produces  all  the  vascular  effects  as 
before,  without  any  secretion  of  saliva  accompanying  them.  Again,  if 
an  animal's  head  be  cut  off,  and  the  chorda  be  rapidly  exposed  and  stimu- 
lated with  an  interrupted  current,  a  secretion  of  saliva  ensues  for  a  short 
time,  although  the  blood  supply  is  necessarily  absent.  These  experiments 
serve  to  prove  that  the  chorda  contains  two  sets  of  nerve  fibres,  one  set 
(vaso-dilator)  which,  when  stimulated,  act  upon  a  local  vaso-motor  centre 
for  regulating  the  blood  supply,  inhibiting  its  action,  and  causing  the 
vessels  to  dilate,  and  so  producing  an  increased  supply  of  blood  to  the 
gland;  while  another  set,  which  are  paralyzed  by  injection  of  atropin, 
directly  stimulate  the  cells  themselves  to  activity,  whereby  they  secrete 
and  discharge  the  constituents  of  the  saliva  which  they  produce.  These 
latter  fibres  very  possibly  terminate  in  the  salivary  cells  themselves.  If, 
on  the  other  hand,  the  sympathetic  fibres  be  divided,  stimulation  of  the 
tongue  by  sapid  substances,  or  of  the  trunk  of  the  lingual,  or  of  the  glosso- 
pharyngeal,  continues  to  produce  a  flow  of  saliva.  From  these  experi- 
ments it  is  evident  that  the  chorda  tympani  nerve  is  the  principal  nerve 
through  which  efferent  impulses  proceed  from  the  centre  to  excite  the 
secretion  of  this  gland. 

The  sympathetic  fibres  appear  to  act  principally  as  a  vaso-constrictor 
nerve,  and  to  exalt  the  action  of  the  local  vaso-motor  centres.  The 
sympathetic  is  more  powerful  in  this  direction  than  the  chorda.  There 
is  not  sufficient  evidence  in  favor  of  the  belief  that  the  submaxillary  gan- 
glion is  ever  the  nerve  centre  which  controls  the  secretion  of  the  sub- 
maxillary  gland. 

B.  On  the  Parotid  Gland. — The  nerves  which  influence  secretion  in 
the  parotid  gland  are  branches  of  the  facial  (lesser  superficial  petrosal)  and 
of  the  sympathetic.  The  former  nerve,  after  passing  through  the  otic 
ganglion,  joins  the  auriculo-temporal  branch  of  the  fifth  cerebral  nerve, 
and,  with  it,  is  distributed  to  the  gland.  The  nerves  by  which  the  stimu- 
lus ordinarily  exciting  secretion  is  conveyed  to  the  medulla  oblongata,  are, 
as  in  the  case  of  the  submaxillary  gland,  the  fifth,  and  the  glossopharyn- 
geal.  The  pneumogastric  nerves  convey  a  further  stimulus  to  the  secre- 
tion of  saliva,  when  food  has  entered  the  stomach;  the  nerve  centre  is  the 
same  as  in  the  case  of  the  submaxillary  gland. 

Changes  in  the  Gland  Cells. — The  method  by  which  the  salivary 
cells  produce  the  secretion  of  saliva  appears  to  be  divided  into  two  stages, 
which  differ  somewhat  according  to  the  class  to  which  the  gland  belongs, 


DIGESTION.  235 

viz.,  (1)  the  true  salivary,  or  (2)  the  mucous  type.  In  the  former  case, 
it  has  been  noticed,  as  has  been  already  described  (p.  228),  that  during 
the  rest  which  follows  an  active  secretion  the  lumen  of  the  alveoli  be- 
comes smaller',  the  gland  cells  larger,  and  very  granular.  During  secre- 
tion the  alveoli  and  their  cells  become  smaller,  and  the  granular  appear- 
ance in  the  latter  to  a  considerable  extent  disappears,  and  at  the  end  of 
secretion,  the  granules  are  confined  to  the  inner  part  of  the  cell  nearest 
to  the  lumen,  which  is  now  quite  distinct  (Fig.  171). 

It  is  supposed  from  these  appearances  that  the  first  stage  in  the  act  of 
secretion  consists  in  the  protoplasm  of  the  salivary  cell  taking  up  from 
the  lymph  certain  materials  from  which  it  manufactures  the  elements  of 
its  own  secretion,  and  which  are  stored  up  in  the  form  of  granules  in  the 
cell  during  rest,  the  second  stage  consisting  of  the  actual  discharge  of 


c 


J\.  r>  \j 

FIG.  171.— Alveoli  of  true  salivary  gland.    A,  at  rest;   B,  in  the  first  stage  of  secretion;  C,  after 
prolonged  secretion.    (Langley.) 


these  granules,  with  or  without  previous  change.  The  granules  are  taken 
to  represent  the  chief  substance  of  the  salivary  secretion,  i.e.,  the  ferment 
ptyalin.  In  the  case  of  the  submaxillary  gland  of  the  dog,  at  any  rate, 
the  sympathetic  nerve-fibres  appear  to  have  to  do  with  the  first  stage  of 
the  process,  and  when  stimulated  the  protoplasm  is  extremely  active  in 
manufacturing  the  granules,  whereas  the  chorda  tympani  is  concerned  in 
the  production  of  the  second  act,  the  actual  discharge  of  the  materials  of 
secretion,  together  with  a  considerable  amount  of  fluid,  the  latter  being 
an  actual  secretion  by  the  protoplasm,  as  it  ceases  to  occur  when  atropin 
has  been  subcutaneously  injected. 

In  the  mucous-secreting  gland,  the  changes  in  the  cells  during  secre- 
tion have  been  already  spoken  of  (p.  228).  They  consist  in  the  gradual 
secretion  by  the  protoplasm  of  the  cell  of  a  substance  called  mucigen, 
which  is  converted  into  mucin,  and  discharged  on  secretion  into  the  canal 
of  the  alveoli.  The  mucigen  is,  for  the  most  part,  collected  into  the 
inner  part  of  the  cells  during  rest,  pressing  the  nucleus  and  the  small 
portion  of  the  protoplasm  which  remains,  against  the  limiting  membrane 
of  the  alveoli. 

The  process  of  secretion  in  the  salivary  glands  is  identical  with  that  of 
glands  in  general;  the  cells  which  line  the  ultimate  branches  of  the  ducts 
being  the  agents  by  which  the  special  constituents  of  the  saliva  are  formed. 


236  HAND-BOOK    OF    PHYSIOLOGY. 

The  materials  which  they  have  incorporated  with  themselves  are  almost 
at  once  given  up  again,  in  the  form  of  a  fluid  (secretion),  which  escapes 
from  the  ducts  of  the  gland;  and  the  cells,  themselves,  undergo  disinte- 
gration,— again  to  be  renewed,  in  the  intervals  of  the  active  exercise  of 
their  functions.  The  source  whence  the  cells  obtain  the  materials  of 
their  secretion,  is  the  blood,  or,  to  speak  more  accurately,  the  plasma, 
which  is  filtered  off  from  the  circulating  blood  into  the  interstices  of  the 
glands  as  of  all  living  textures. 

THE  PHARYNX. 

That  portion  of  the  alimentary  canal  which  intervenes  between  the 
mouth  and  the  oesophagus  is  termed  the  Pharynx  (Fig.  165).  It  will 
suffice  here  to  mention  that  it  is  constructed  of  a 
series  of  three  muscles  with  striated  fibres  (constrict- 
ors), which  are  covered  by  a  thin  fascia  externally, 
and  are  lined  internally  by  a  strong  fascia  (pharyn- 
geal  aponeurosis),  on  the  inner  aspect  of  which  is 
areolar  (submucous)  tissue  and  mucous  membrane, 
continuous  with  that  of  the  mouth,  and,  as  regards 
the  part  concerned  in  swalloAving,  is  identical  with 
i^  in  general  structure.  The  epithelium  of  this  part 
of  the  Pharynx,  like  that  of  the  mouth,  is  stratified 

brane   with   its  papillae;       nr\(\  cminrnrmss 
6,  lymphoid  tissue,  with      an°  US' 

(Key8)  lymphoid  sacs-  The  pharynx  is  well  supplied  with  mucous  glands 
(Fig.  174). 

The  Tonsils. — Between  the  anterior  and  posterior  arches  of  the  soft 
palate  are  situated  the  Tonsils,  one  on  each  side.  A  tonsil  consists  of  an 
elevation  of  the  mucous  membrane  presenting  12  to  15  orifices,  which  lead 
into  crypts  or  recesses,  in  the  walls  of  which  are  placed  nodules  of  adenoid 
or  lymphoid  tissue  (Fig.  173).  These  nodules  are  enveloped  in  a  less 
dense  adenoid  tissue  which  reaches  the  mucous  surface.  The  surface  is 
covered  with  stratified  squamous  epithelium,  and  the  subepithelial  or 
mucous  membrane  proper  may  present  rudimentary  papillse  formed  of 
adenoid  tissue.  The  tonsil  is  bounded  by  a  fibrous  capsule  (Fig.  173,  e). 
Into  the  crypts  open  a  number  of  ducts  of  mucous  glands. 

The  viscid  secretion  which  exudes  from  the  tonsils  serves  to  lubricate 
the  bolus  of  food  as  it  passes  them  in  the  second  part  of  the  act  of  degluti- 
tion. 

THE  (ESOPHAGUS  OR  GULLET. 

The  (Esophagus  or  Gullet  (Fig.  165),  the  narrowest  portion  of  the 
alimentary  canal,  is  a  muscular  and  mucous  tube,  nine  or  ten  inches  in 
length,  which  extends  from  the  lower  end  of  the  pharynx  to  the  cardiac 
orifice  of  the  stomach. 


DIGESTION. 


237 


Structure. — The  oesophagus  is  made  up  of  three  coats — viz.,  the  outer, 
mscular;  the  middle,  submucous;  and  the  inner,  mucous.  The  mus- 
cular coat  (Fig.  175,  g  and  i)  is  covered  externally  by  a  varying  amount 
>f  loose  fibrous  tissue.  It  is  composed  of  two  layers  of  fibres,  the  outer 
?ing  arranged  longitudinally,  and  the  inner  circularly.  At  the  upper 
part  of  the  oesophagus  this  coat  is  made  up  principally  of  striated  muscle 
fibres,  as  they  are  continuous  with  the  constrictor  muscles  of  the  pharynx; 
but  lower  down  the  unstriated  fibres  become  more  and  more  numerous,  and 
toward  the  end  of  the  tube  form  the  entire  coat.  The  muscular  coat  is 
connected  with  the  mucous  coat  by  a  more  or  less  developed  layer  of 


FIG.  173.— Vertical  section  through  a  crypt  of  the  human  tonsil,  a,  entrance  to  the  crypt,  which 
is  divided  below  by  the  elevation  which  does  not  quite  reach  the  surface ;  6,  stratified  epithelium ;  c, 
masses  of  adenoid  tissue;  d,  mucous  glands  cut  across;  e,  fibrous  capsule.  (V.  D.  Harris.) 

areolar  tissue,  which  forms  the  submucous  coat  (Fig  175,  /),  in  which  is 
contained  in  the  lower  half  or  third  of  the  tube  many  mucous  glands,  the 
ducts  of  which,  passing  through  the  mucous  membrane  (Fig.  175,  c)  open 
on  its  surface.  Separating  this  coat  from  the  mucous  membrane  proper 
is  a  well-developed  layer  of  longitudinal,  unstriated  muscle  (d),  called 
the  muscular  is  mucosce.  The  mucous  membrane  is  composed  of  a  closely 
felted  meshwork  of  fine  connective  tissue,  which,  toward  the  surface,  is 
elevated  into  rudimentary  papillae.  It  is  covered  with  a  stratified  epithe- 
lium, of  which  the  most  superficial  layers  are  squamous.  The  epithelium 
is  arranged  upon  a  basement  membrane. 

In  newly-born  children  the  mucous  membrane  exhibits,  in  many  parts, 
the  structure  of  lymphoid  tissue  (Klein). 

Blood  and  lymph  vessels,  and  nerves,  are  distributed  in  the  walls  of 
the  oesophagus.  Between  the  outer  and  inner  layers  of  the  muscular  coat, 
nerve-ganglia  of  Auerbach  are  also  found. 


238 


HAND-BOOK    OF    PHYSIOLOGY. 


DEGLUTITION  OR  SWALLOWING. 

When  properly  masticated,  the  food  is  transmitted  in  successive  por- 
tions to  the  stomach  by  the  act  of  deglutition  or  swallowing.  This,  for 
the  purpose  of  description,,  may  be  divided  into  three  acts.  In  the  first, 
particles  of  food  collected  to  a  morsel  are  made  to  glide  between  the  sur- 
face of  the  tongue  and  the  palatine  arch,  till  they  have  passed  the  anterior 
arch  of  the  fauces;  in  the  second,  the  morsel  is  carried  through  the 


FIG.  174. 


FIG.  175. 


FIG.  174. — Section  of  a  mucous  gland  from  the  tongue.  A,  opening  of  the  duct  on  the  free  sur- 
face; C,  basement  membrane  with  nuclei;  B,  flattened  epithelial  cells  lining  duct.  The  duct  divides 
into  several  branches,  which  are  convoluted  and  end  blindly,  being  lined  throughout  by  columnar 
epithelium.  D,  lumen  of  one  of  the  tubuli  of  the  gland,  x  !X).  (Klein  and  Noble  Smith.) 

FIG.  175. — Longitudinal  section  of  oesophagus  of  a  dog  toward  the  lower  end.  a,  stratified  epithe- 
lium of  the  mucous  membrane;  6,  mucous  membrane  proper;  c,  duct  of  mucous  gland;  d,  muscu- 
laris  mucosae ;  e,  mucous  glands;/,  submucous  coat;  g,  circular  muscular  layer;  /i,  intermuscular 
layer,  in  which  is  contained  the  ganglion  cells  of  Auerbach;  i,  longitudinal  muscular  layer;  A-,  outside 
investment  of  fibrous  tissue.  X  100.  (V.  D.  Harris.) 

pharynx;  and  in  the  third,  it  reaches  the  stomach  through  the  oesophagus. 
These  three  acts  follow  each  other  rapidly.  (1.)  Tli3  first  act  of  deglutition 
may  be  voluntary,  although  it  is  usually  performed  unconsciously;  the 
morsel  of  food,  when  sufficiently  masticated,  being  pressed  between  the 
tongue  and  palate,  by  the  agency  of  the  muscles  of  the,  former,  in  such 
a  manner  as  to  force  it  back  to  the  entrance  of  the  pharynx.  (2. )  The 
second  act  is  the  most  complicated,  because  the  food  must  pass  by  the 


DIGESTION.  239 

posterior  orifice  of  the  nose  and  the  upper  opening  of  the  larynx  without 
mching  them.  When  it  has  been  brought,  by  the  first  act,  between  the 
anterior  arches  of  the  palate,  it  is  moved  onward  by  the  movement  of 
the  tongue  backward,  and  by  the  muscles  of  the  anterior  arches  contract- 
ing on  it  and  then  behind  it.  The  root  of  the  tongue  being  retracted, 
and  the  larynx  being  raised  with  the  pharynx  and  carried  forward  under 
the  base  of  the  tongue,  the  epiglottis  is  pressed  over  the  upper  opening 
>f  the  larynx,  and  the  morsel  glides  past  it;  the  closure  of  the  glottis 
being  additionally  secured  by  the  simultaneous  contraction  of  its  own  mus- 
cles: so  that,  even  when  the  epiglottis  is  destroyed,  there  is  little  danger 
of  food  or  drink  passing  into  the  larynx  so  long  as  its  muscles  can  act 
freely.  At  the  same  time,  the  raising  of  the  soft  palate,  so  that  its  pos- 
terior edge  touches  the  back  part  of  the  pharynx,  and  the  approximation 
of  the  sides  of  the  posterior  palatine  arch,  which  move  quickly  inward 
like  side  curtains,  close  the  passage  into  the  upper  part  of  the  pharynx  and 
the  posterior  nares,  and  form  an  inclined  plane,  along  the  under  surface 
of  which  the  morsel  descends;  then  the  pharynx,  raised  up  to  receive  it, 
in  its  turn  contracts,  and  forces  it  omvard  into  the  oesophagus.  (3.)  In 
the  third  act,  in  which  the  food  passes  through  the  oesophagus,  every 
part  of  that  tube,  as  it  receives  the  morsel  and  is  dilated  by  it,  is  stimu- 
lated to  contract:  hence  an  undulatory  contraction  of  the  oesophagus, 
which  is  easily  observable  in  horses  while  drinking,  proceeds  rapidly  along 
the  tube.  It  is  only  when  the  morsels  swallowed  are  large,  or  taken  too 
fjiiickly  in  succession,  that  the  progressive  contraction  of  the  oesophagus 
is  slow,  and  attended  with  pain.  Division  of  both  pnetimogastric  nerves 
paralyzes  the  contractile  power  of  the  oesophagus,  and  food  accordingly 
accumulates  in  the  tube.  The  second  and  third  parts  of  the  act  of  deglu- 
tition are  involuntary. 

Nerve  Mechanism. — The  nerves  engaged  in  the  reflex  act  of  deglu- 
tition are: — sensory,  branches  of  the  fifth  cerebral  supplying  the  soft 
} Dilate;  glosso-pharyngeal,  supplying  the  tongue  and  pharynx;  the  supe- 
rior laryngeal  branch  of  the  vagus,  supplying  the  epiglottis  and  the  glot- 
tis; while  the  motor  fibres  concerned  are: — branches  of  the  fifth,  supply- 
ing part  of  the  digastric  and  mylo-hyoid  muscles,  and  the  muscles  of 
mastication;  the  facial,  supplying  the  levator  palati;  the  glosso-pharyn- 
geal, supplying  the  muscles  of  the  pharynx;  the  vagus,  supplying  the 
muscles  of  the  larynx  through  the  inferior  laryngeal  branch,  and  the 
hypoglossal,  the  muscles  of  the  tongue.  The  nerve-centre  by  which 
the  muscles  are  harmonized  in  their  action,  is  situate  in  the  medulla 
oblongata.  In  the  movements  of  the  oesophagus,  the  ganglia  contained 
in  its  walls,  with  the  pneumogastrics,  are  the  nerve-structures  chiefly 
concerned. 

It  is  important  to  note  that  the  swallowing  both  of  food  and  drink  is  a 
muscular  act,  and  can,  therefore,  take  place  in  opposition  to  the  force  of 


:)  10  ii  ANIM-.OOK    OK    PHYSIOLOGY. 

gravity,    Tims,  borrti 'and  many  other  animals  habitually  drink  uphill, 

and  the  same  teat  can  he  performed  hy  jui^lers. 

TIIK  STOMACH. 

In  man  and  t  hose  Mammalia  which  are  provided  with  a  :  in"  lc  stomach, 
il  consists  of  a  dilatation  of  t  he  alimentary  canal  placed  het  ween  and  con 
Millions  \\  il  1 1  t  he  (csophaiMis.  which  enters,  its  larger  or  card  iac  end  on  t  he 
one  hand,  and  the  small  intestine,  which  commences  at  its,  narrowed  end 
or  p\  lorus,  on  I  he  oilier.  It  \aries  in  shape  and  si/.e  accordini','  to  its 
state  of  distension. 

The   Ifiunhnuils  (o\,  sheep,  deer,  etc.)   possess  \er\    romple\  stomachs; 
in  most  of  them  four  distinct  cavities  are  to  be  distinguished  ( l;i"   I'iil). 

I.    The  run  iifh  or    l\iiin<  H,  a  \  cr\    larrc  ca\  il  \    \\  In. 'h  occupies  I  he  car 
diac  end,  and    into  \\hich  lar^e  <|uanlities  of  food  are  in  the  lirst   instance 
s\\  allowed  \\ilh    little  or  no   mast  icat  i(»n.      ?.    The    /h'/int/tnii,  or    //onti/- 
((»///>  stomach,  so  called   from  the    fact    I  hat    its  inn  eon.-;    memhrane    i. 
posed  in  a  numherol  folds  enclosing  hexagonal  cells.     ','>.    The  / 


•JtfC 


I'h.     I  •;•«*,      Sl,iin:i,-h..i      IH-.-I.      ,,      .,-  -.,.|.l.:ii-.n-..    K,t.    ruinrn,    /;,  •/.    ivl  i.-iiliiiii;    7V.   l»s.'ill.M-itnn,    or 
•      ;   .l.iilioniMMiin.    /),,., luo,r,-miiu;  ,/.  KI-,.,.V»- froiii  .i-s.-pliiiKUN  I..  psnll.Tllim.     (lluxlvy.) 


or  Mitni/fifft'ti,  iii  \vhi«-h  I  he  mucous  memhrane  is  MrrMU^ed  in  very  promi- 
nent longitudinal  folds.  -I.  .l/>tnnnsnni.  lu'cd.  or  lit'/tticf,  narrow  and 
elongated,  its  mucous  incmhrane  hcin^  much  more  hi"hl\  vascular  than 
thai  of  the  other  divisions.  In  the  process  of  rumination  small  portions 
of  the  contents  of  the  rumen  and  rclictilum  are  siiccessi\  el  \  rejMirv.ilalcd 
illlo  the  month,  and  there  Miorouj-Jdv  ma.licalcd  and  insalivated  (chew 
iii'  ihccud):  Miev  are  then  a.",ain  s\\  allon  cd,  heni",  this  lime  directed  hy 
a  L^roo\e  (\\hich  in  the  li;Mirc  is  seen  runnin.i>,  from  the  lower  end  of  the 
(esophagus)  inlo  lht>  main  plies,  and  thence  into  the  ahomasuiu.  It  \\ill 
thus  he  seen  that  the  lirst,  t  \\  o  stomachs  (paunch  and  retieulum)  have 
ehicllv  the-  mechanical  functions  of  storing  and  moistening  t  lie  fodder:  the 
third  (mainplies)  prohahlx  ads  as  a  st  raiucr.  only  allouin:1;  the  linely 
divide*!  portions  of  food  to  pass  on  into  the  fourth  stomach,  when1  the 
":i  inc  juice  is  secreted  and  the  process  of  digestion  carried  on.  The 
mucous  memhrane  of  the  first  three  stomachs  is  lowly  \ascular,  while  that 
of  tht'  fourth  is  pulpy,  glandular,  and  highly  vascular. 

In  some  ot  her  animals,  as  the  pi."  .  a  similar  (list  i  net  ion  obtains  het  w  ecu 
the  mucous  memhrane  in  dilTercnl   parts  of  the  stomach. 


Ill    the   piu"    the    ;d;ind  •    in    (he    cardiac    end  are    few  and    small,   while 
toward  the  p\  lorns  they  arc  abundant  and  lar^e. 

A    similar   division    of    I  he    stomach    into    a    cardiac    (receptive)    and    a 
p\  loric    (digestive)    parl.     foreshadowing    the   complex     slomach    of     riiini 
naiiK  is   seen    in    I  he  common    nil,  in    which  these    t  \\  •  •  d  i\  i.  ion ,;  of    the 
.stomach    are    distinguished,    nol    only    by    the    characlers    of    (heir   lining 
membrane,  but  also  Iry  a  well  marked  constriction. 

In  birds  the  function  of  mastication  is  performed  bv  the  stomach  (^'i/- 

/ard)  which    in   grauivoroUH  orders,  c.</.   the  conn i    fo\\l,  pos.-es.es  \er\ 

powerful  muscular  \\allsand  a  dense  horny  epithelium. 

Structure. — Tim  stomach  is  composed  of  four  coats,  called  respeo- 

ti\elv  an  external  or  (I)  /H'i'i/oin  ,>  .  I  ')  nuixrnltu\  (i5)  sH/inmrtm*.  and 
(I)  mucous  Milt \  with  blood  ve  ids,  l\  mphatics,  and  nerves  d  i  !  nbiilc.l  m 
and  bet  ween  them. 

(1)    The  fn'i-ilniinil  coat.  IIM  '  rucluiv  of  serous  membrane    in  veil 

era!   (p.   :>l'.l).       (I)    The  iiuisculitr  coal  consists  of    Mirce  separate  la\e|'80r 
.   which,  according  to  their  several  directions,  are    named  the 

ilmlinal,    eiivnlar.  and    ohli(|iu).      The    faiujit utliiHtl  set  are  the    most 
superficial:  Miey  are  cont  inuoiis  wilh  the  longitudinal   libre.s  of  t  he  o-: oph 

.   and    spread  out    in    a.    dmTviii"    manner  uverlhe   cardiac   end    and 
'omach.      They  extend  as  far  a:-  1  he  p\  lorn;1,  heinn  especial  I  \ 
distinct    at    the    lesser  or   Upper   Clir\alnrc  of   the  slomaeh,    alonv    \\hieli 
they  PM  ';d  si  roii"  bands.      The  next  set  are  I  he  rircnhir  or  tritH*- 

wrM'    fibres,  which    more    or   less  completely    encircle    all     parts    of    the 
stomach;    they  are  most  abundant  at.  1  he  middle  MI  id   in  I  he  p\  lorn-  port  ion 
of  the  •.!•;•  MII.  and  form  the  chief   parl.  of  t  he  t  hiek    projecting  ring  of  the 
pylorus.      These  tibi-es  are   not,  simple    circles,  but,    form  double  or  figure 
of  S    loops,  t  be   fibre-:    i  1 1 1  c  i'  .  •(•(  i  IIM;    very   obliquely.      The    next,    and    con 

lently  deepest  set,  of  fibres,  are  the  oblique,  continuous  with  the  <  n 

cular  miisr-nlar  fibres  of  the  oesophagus,  and   having  the  same  double- 

lo.i|iei|  ai Taiiycment .  1  luj.l,  prevails  in  the  pi-ecediiiL1:  layer:  they  are  eom- 
p;irati\el\  few  in  number,  and  are  placed  only  at  the  cardiac  orifice  and 
portion  of  1  he  slomach,  over  both  surfaces  of  which  Ihev  are  spread,  ;ome 

'.hlii|iiel\  from   left  to  rij-ht,  others  from  ri^ht  to  left,  around  the 
'•anliae    (.rilice,     to    which,    by    llu-ir   interlacing,    they    form    a     kind    of 

sphincter,  continuous  with  that  around  the  h.wor  end  of  the  oosoplu^iiH. 

The  muscular  fibres  of  i  he     t  omach  and  of  t  he  intestinal  canal  arc  tin  sin 
"/'•'/.  l.'ciiij  on.iraled,  spindle-shaped  libre-cell  . 

(;!)  and  (  I)  The  mucous  membrane  of  tin  st<imach,  which  rests  upon  a. 

I:')'-!'  of  loo'e  cellular  membrane,  or  xulniiiicoiis  tissue,  is  smooth,  Ic-vc'l, 
soft,  and  velvety;  of  a  pale  pink  color  during  life,  and  in  the  contracted 
Btate  thrown  info  numerous-,  ehiell\  longitudinal,  b'ld  or  ru^e,  \\hich 

disappear  when  the  organ  Is  di  tended. 

fhe  basis   of  the  mucous    membrane    is  a.  film  connective  tissue,   which 
loscly  in  structure  to  adenoid  tissue;    this  tissue   supports  the 
\'oi,     I.— 1(J. 


242  HAND-BOOK    OF    PHYSIOLOGY. 

tabular  glands  of  which  the  superficial  and  chief  part  of  the  mucous 
membrane  is  composed,  and  passing  up  between  them  assists  in  binding 
them  together.  Here  and  there  are  to  be  found  in  this  coat,  immediately 
underneath  the  glands,  masses  of  adenoid  tissue  sufficiently  marked  to 
be  termed  by  some  lymphoid  follicles.  The  glands  are  separated  from 
the  rest  of  the  mucous  membrane  by  a  very  fine  homogeneous  basement 
membrane. 

At  the  deepest  part  of  the  mucous  membrane  are  two  layers  (circular  and 
longitudinal)  of  unstriped  muscular  fibres,  called  the  muscularis  mucoscv, 
which  separate  the  mucous  membrane  from  the  scanty  submucous  tissue. 

When  examined  with  a  lens,  the  internal  or  free  surface  of  the  stomach 
presents  a  peculiar  honeycomb  appearance,  produced  by  shallow  polygo- 
nal depressions,  the  diameter  of  which  varies  generally  from  ,-}T  th  to 
-g-l-g-th  of  an  inch;  but  near  the  pylorus  is  as  much  as  y^-th  of  an  inch. 
They  are  separated  by  slightly  elevated  ridges,  which  sometimes,  especially 
in  certain  morbid  states  of  the  stomach,  bear  minute,  narrow  vascular 
processes,  which  look  like  villi,  and  have  given  rise  to  the  erroneous  sup- 
position that  the  stomach  has  absorbing  villi,  like  those  of  the  small  in- 
testines. In  the  bottom  of  these  little  pits,  and  to  some  extent  between 
them,  minute  openings  are  visible,  which  are  the  orifices  of  the  ducts  of 
perpendicularly  arranged  tubular  glands  (Fig.  177),  imbedded  side  by 
side  insets  or  bundles,  on  the  surface  of  the  mucous  membrane,  and 
composing  nearly  the  whole  structure. 

Gastric  Glands. — Of  these  there  are  two  varieties,  (a)  Peptic,  (b) 
Pyloric  or  Mucous. 

(a)  Peptic  glands  are  found  throughout  the  whole  of  the  stomach  except 
at  the  pylorus.  They  are  arranged  in  groups  of  four  or  five,  which  are 
separated  by  a  fine  connective  tissue.  Two  or  three  tubes  often  open  into 
one  duct,  which  forms  about  a  third  of  the  whole  length  of  the  tube  and 
opens  on  the  surface.  The  ducts  are  lined  with  columnar  epithelium. 
Of  the  gland  tube  proper,  i.e.,  the  part  of  the  gland  below  the  duct,  the 
upper  third  is  the  neck  and  the  rest  the  body.  The  neck  is  narrower 
than  the  body,  and  is  lined  with  granular  cubical  cells  which  are  continu- 
ous with  the  columnar  cells  of  the  duct.  Between  these  cells  and  the 
membrana  propria  of  the  tubes,  are  large  oval  or  spherical  cells,  opaque 
or  granular  in  appearance,  with  clear  oval  nuclei,  bulging  out  the  mem- 
brana propria;  these  cells  are  called  peptic  or  parietal  cells.  They  do  not 
form  a  continuous  layer.  The  body,  which  is  broader  than  the  neck  and 
terminates  in  a  blind  extremity  or  fundus  near  the  muscularis  mucosae, 
is  lined  by  cells  continuous  with  the  cubical  or  central  cells  of  the  neck, 
but  longer,  more  columnar  and  more  transparent.  In  this  part  are  a  few 
parietal  cells  of  the  same  kind  as  in  the  neck  (Fig.  177). 

As  the  pylorus  is  approached  the  gland  ducts  become  longer,  and  the 
tube  proper  becomes  shorter,  and  occasionally  branched  at  the  fundus. 


DIGESTION. 


243 


(b)  Pyloric  Glands. — These  glands  (Fig.  179)  have  much  longer  ducts 
than  the  peptic  glands.  Into  each  duct  two  or  three  tubes  open  by  very 
short  and  narrow  necks,  and  the  body  of  each  tube  is  branched,  wavy, 
and  convoluted.  The  lumen  is  very  large.  The  ducts  are  lined  with 
columnar  epithelium,,  and  the  neck  and  body  with  shorter  and  more  gran- 


FIG.  178. 


FIG.  179. 

FIG.  177.— From  a  vertical  section  through  the  mucous  membrane  of  the  cardiac  end  of  stomach. 
Two  peptic  glands  are  shown  with  a  duct  common  to  both,  one  gland  only  in  part,  a,  duct  with  col- 
umnar epithelium  becoming  shorter  as  the  cells  are  traced  downward;  n,  neck  of  gland  tubes,  with 
central  and  parietal  or  so-called  peptic  cells;  6,  fundus  with  curved  cspcal  extremity— the  parietal  cells 
are  not  so  numerous  here.  X  400.  (Klein  and  Noble  Smith.) 

FIG.  178. — Transverse  section  through  lower  part  of  peptic  glands  of  a  cat.  a,  peptic  cells;  6, 
small  spheroidal  or  cubical  cells;  c,  transverse  section  of  capillaries.  (Frey.) 

FIG.  179.— Section  showing  the  pyloric  glands.  s,  free  surf  ace;  d,  ducts  of  pyloric  glands ;  n,  neck 
of  same;  «i,  the  gland  alveoli;  m  m,  muscularis  mucosae.  (Klein  and  Noble  Smith.) 

ular  cubical  cells,  which  correspond  with  the  central  cells  of  the  peptic 
glands.  During  secretion  the  cells  become,  as  in  the  case  of  the  peptic 
glands,  larger  and  the  granules  restricted  to  the  inner  zone  of  the  cell. 
As  they  approach  the  duodenum  the  pyloric  glands  become  larger,  more 


244  HAND-BOOK    OF    PHYSIOLOGY. 

convoluted  and  more  deeply  situated.     They  are  directly  continuous  with 
Brunner's  glands  in  the  duodenum.     (Watney.) 

Changes  in  the  gland  cells  during  secretion. — The  chief  or  cubical  cells 
of  the  peptic  glands,  and  the  corresponding  cells  of  the  pyloric  glands 
during  the  early  stage  of  digestion,  if  hardened  in  alcohol,  appear  swollen 
and  granular,  and  stain  readily.  At  a  later  stage  the  cells  become 
smaller,  but  more  granular  and  stain  even  more  readily.  The  parietal 
cells  swell  up,  but  are  otherwise  not  altered  during  digestion.  The  gran- 
ules, however,  in  the  alcohol-hardened  specimen,  are  believed  not  to  exist 
in  the  living  cells,  but  to  have  been  precipitated  by  the  hardening  re- 
agent; for  if  examined  during  life  they  appear  to  be  confined  to  the  inner 
zone  of  the  cells,  and  the  outer  zone  is  free  from  granules,  whereas  during 
rest  the  cell  is  granular  throughout.  These  granules  are  thought  to  be 


FIG.  180.— Plan  of  the  blood-vessels  of  the  stomach,  as  they  would  be  seen  in  a  vertical  section, 
a,  arteries,  passing  up  from  the  vessels  of  submucous  coat;  6,  capillaries  branching  between  and 
around  the  tubes;  c,  superficial  plexus  of  capillaries  occupying  the  ridges  of  the  mucous  membrane; 
d,  vein  formed  by  the  union  of  veins  which,  having  collected  the  blood  of  the  superficial  capillary 
plexus,  are  seen  passing  down  between  the  tubes.  (Brinton.) 

pepsin,  or  the  substance  from  which  pepsin  is  formed,  pepsinogen,  which 
is  during  rest  stored  chiefly  in  the  inner  zone  of  the  cells  and  discharged 
into  the  lumen  of  the  tube  during  secretion.  (Langley.) 

Lymphatics. — Lymphatic  vessels  surround  the  gland  tubes  to  a  greater 
or  less  extent.  Toward  the  fundus  of  the  peptic  glands  are  found  masses 
of  lymphoid  tissue,  which  may  appear  as  distinct  follicles,  somewhat  like 
the  solitary  glands  of  the  small  intestine. 

Blood-vessels. — The  blood-vessels  of  the  stomach,  which  first  break  up 
in  the  submucous  tissue,  send  branches  upward  between  the  closely 
packed  glandular  tubes,  anastomosing  around  them  by  means  of  a  fine 
capillary  network,  with  oblong  meshes.  Continuous  with  this  deeper 
plexus,  or  prolonged  upward  from  it,  so  to  speak,  is  a  more  superficial 
network  of  larger  capillaries,  which  branch  densely  around  the  orifices 


DIGESTION.  245 

of  the  tubes,  and  form  the  framework  on  which  are  moulded  the  small 
elevated  ridges  of  mucous  membrane  bounding  the  minute,  polygonal 
pits  before  referred  to.  From  this  superficial  network  the  veins  chiefly 
take  their  origin.  Thence  passing  down  between  the  tubes,  with  no  very 
free  connection  with  the  deeper  inter-tubular  capillary  plexus,  they  open 
finally  into  the  venous  network  in  the  submucous  tissue. 

Nerves. — The  nerves  of  the  stomach  are  derived  from  the  pneu mo- 
gastric  and  sympathetic,  and  form  a  plexus  in  the  submucous  and  mus- 
cular coats,  containing  many  ganglia  (Remak,  Meissner). 

DIGESTION  IN  THE  STOMACH. 

Gastric  Juice. — The  functions  of  the  stomach  are  to  secrete  a  diges- 
tive fluid  (gastric'  juice),  to  the  action  of  which  the  food  is  next  subjected 
after  it  has  entered  the  cavity  of  the  stomach  from  the  oesophagus;  to 
thoroughly  incorporate  the  fluid  with  the  food  by  means  of  its  muscular 
movements;  and  to  absorb  such  substances  as  are  capable  of  absorption. 
While  the  stomach  contains  no  food,  and  is  inactive,  no  gastric  fluid  is 
secreted;  and  mucus,  which  is  either  neutral  or  slightly  alkaline,  covers 
its  surface.  But  immediately  on  the  introduction -of  food  or  other  sub- 
stance the  mucous  membrane,  previously  quite  pale,  becomes  slightly 
turgid  and  reddened  with  the  influx  of  a  larger  quantity  of  blood;  the 
gastric  glands  commence  secreting  actively,  and  an  acid  fluid  is  poured 
out  in  minute  drops,  which  gradually  run  together  and  flow  down  the 
walls  of  the  stomach,  or  soak  into  the  substances  within  it. 

Chemical  Composition  of  Gastric  Juice. — The  first  accurate 
analysis  of  gastric  juice  was  made  by  Prout:  but  it  does  not  appear  to 
have  been  collected  in  any  large  quantity,  or  pure  and  separate  from  food, 
until  the  time  when  Beaumont  was  enabled,  by  a  fortunate  circumstance, 
to  obtain  it  from  the  stomach  of  a  man  named  St.  Martin,  in  whom  there 
existed,  as  the  result  of  a  gunshot  wound,  an  opening  leading  directly 
into  the  stomach,  near  the  upper  extremity  of  the  great  curvature,  and 
three  inches  from  the  cardiac  orifice.  The  introduction  of  any  mechanical 
irritant,  such  as  the  bulb  of  a  thermometer,  into  the  stomach,  excited  at 
once  the  secretion  of  gastric  fluid.  This  was  drawn  off,  and  was  often 
obtained  to  the  extent  of  nearly  an  ounce.  The  introduction  of  aliment- 
ary substances  caused  a  much  more  rapid  and  abundant  secretion  than 
did  other  mechanical  irritants.  Xo  increase  of  temperature  could  be 
detected  during  the  most  active  secretion;  the  thermometer  introduced 
into  the  stomach  always  stood  at  100°  F.  (37*8°  C.)  except  during  muscu- 
lar exertion,  when  the  temperature  of  the  stomach,  like  that  of  other 
parts  of  the  body,  rose  one  or  two  degrees  higher. 

The  chemical  composition  of  human  gastric  juice  has  been  also  in- 
vestigated by  Schmidt.  The  fluid  in  this  case  was  obtained  by  means  of  an 


246  HAND-BOOK    OF    PHYSIOLOGY. 

accidental  gastric  fistula,  which  existed  for  several  years  below  the  left 
mammary  region  of  a  patient  between  the  cartilages  of  the  ninth  and 
tenth  ribs.  The  mucous  membrane  was  excited  to  action  by  the  introduc- 
tion of  some  hard  matter,  such  as  dry  peas,  and  the  secretion  was  removed 
by  means  of  an  elastic  tube.  The  fluid  thus  obtained  was  found  to  be  acid, 
limpid,  odorless,  with  a  mawkish  taste — with  a  specific  gravity  of  1002, 
or  a  little  more.  It  contained  a  few  cells,  seen  with  the  microscope,  and 
some  fine  granular  matter.  The  analysis  of  the  fluid  obtained  in  this  is 
given  below.  The  gastric  juice  of  dogs  and  other  animals  obtained  by 
the  introduction  into  the  stomach  of  a  clean  sponge  through  an  artifi- 
cially made  gastric  fistula,  shows  a  decided  difference  in  composition,  but 
possibly  this  is  due,  at  least  in  part,  to  admixture  with  food. 

CHEMICAL  COMPOSITION  OF  GASTRIC  JUICE. 

Dogs.  Human. 

Water 971-17  994-4 

Solids  28-82  5  "39 


Solids- 
Ferment— Pepsin  .         .         .  17'5  3*19 
Hydrochloric  acid  (free}         ....2*7  -2 

Salts- 
Calcium,  sodium,  and  potassium,  chlorides;  and 
calcium,  magnesium,  and  iron,  phosphates     .     8*57  2 '19 


The  quantity  of  gastric  juice  secreted  daily  has  been  variously  esti- 
mated; but  the  average  for  a  healthy  adult  may  be  assumed  to  range  from 
ten  to  twenty  pints  in  the  twenty-four  hours.  The  acidity  of  the  fluid  is 
due  to  free  hydrochloric  acid,  although  other  acids,  e.g.,  lactic,  acetic, 
butyric,  are  not  unfrequently  to  be  found  therein  as  products  of  gastric 
digestion.  The  amount  of  hydrochloric  acid  varies  from  2  to  '2  per  1000 
parts.  In  healthy  gastric  juice  the  amount  of  free  acid  may  be  as  much 
as  *2  per  cent. 

As  regards  the  formation  of  pepsin  and  acid,  the  former  is  produced 
by  the  central  or  chief  cells  of  the  peptic  glands,  and  also  most  likely  by 
the  similar  cells  in  the  pyloric  glands;  the  acid  is  chiefly  found  at  the 
surface  of  the  mucous  membrane,  but  is  in  all  probability  formed  by  the 
secreting  action  of  the  parietal  cells  of  the  peptic  glands,  as  no  acid  is 
formed  by  the  pyloric  glands  in  which  this  variety  of  cell  is  absent. 

The  ferment  Pepsin  (p.  246)  can  be  procured  by  digesting  portions 
of  the  mucous  membrane  of  the  stomach  in  cold  water,  after  they  have 
been  macerated  for  some  time  in  water  at  a  temperature  80° — 100°  F. 
(27  •« — 37 '8°  C.).  The  warm  water  dissolves  various  substances  as  well 
as  some  of  the  pepsin,  but  the  cold  water  takes  up  little  else  than  pepsin, 
which  is  contained  in  a  greyish-brown  viscid  fluid,  on  evaporating  the 


DIGESTION. 


247 


cold  solution.  The  addition  of  alcohol  throws  down  the  pepsin  in  greyish- 
white  flocculi.  Glycerine  also  has  the  property  of  dissolving  out  the  fer- 
ment; and  if  the  mucous  membrane  be  finely  minced  and  the  moisture 
removed  by  k absolute  alcohol,  a  powerful  extract  may  be  obtained  by 
tin-owing  into  glycerine. 

Functions. — The  digestive  power  of  the  gastric  juice  depends  on  the 
pepsin  and  acid  contained  in  it,  both  of  which  are,  under  ordinary  cir- 
cumstances, necessary  for  the  process. 

The  general  effect  of  digestion  in  the  stomach  is  the  conversion  of 
the  food  into  chyme,  a  substance  of  various  composition  according  to  the 
nature  of  the  food,  yet  always  presenting  a  characteristic  thick,  pultace- 
ous,  grumous  consistence,  with  the  undigested  portions  of  the  food  mixed 
in  a  more  fluid  substance,  and  a  strong,  disagreeable  acid  odor  and  taste. 

The  chief  function  of  the  gastric  juice  is  to  convert  proteids  into  pep- 
tones. This  action  may  be  shown  by  adding  a  little  gastric  juice  (natural 
or  artificial)  to  some  diluted  egg-albumin,  and  keeping  the  mixture  at  a 
temperature  of  about  100°  F.  (37*8°  C.);  it  is  soon  found  that  the  albu- 
min cannot  be  precipitated  on  boiling,  but  that  if  the  solution  be  neutral- 
ized with  an  alkali,  a  precipitate  of  acid-albumin  is  thrown  down.  After 
a  while  the  proportion  of  acid-albumin  gradually  diminishes,  so  that  at 
last  scarcely  any  precipitate  results  on  neutralization,  and  finally  it  is 
found  that  all  the  albumin  has  been  changed  into  another  proteid  sub- 
stance which  is  not  precipitated  on  boiling  or  on  neutralization.  This  is 
called  peptone. 

Characteristics  of  Peptones. — Peptones  have  certain  characteristics 
which  distinguish  them  from  other  proteids.  1.  They  are  diffusible,  i.e., 
they  possess  the  property  of  passing  through  animal  membranes.  2. 
They  cannot  be  precipitated  by  heat,  nitric,  or  acetic  acid,  or  potassium 
ferrocyanide  and  acetic  acid.  They  are,  however,  thrown  down  by  tannic 
acid,  by  mercuric  chloride  and  by  picric  acid.  3.  They  are  very  soluble 
in  water  and  in  neutral  saline  solutions. 

In  their  diff visibility  peptones  differ  remarkably  from  egg-albumin, 
and  on  this  diffusibility  depends  one  of  their  chief  uses.  Egg-albumin  as 
such,  even  in  a  state  of  solution,  would  be  of  little  service  as  food,  inas- 
much as  its  indiffusibility  would  effectually  prevent  its  passing  by  absorp- 
tion into  the  blood-vessels  of  the  stomach  and  intestinal  canal.  Changed, 
however,  by  tha  action  of  the  gastric  juice  into  peptones,  albuminous 
matters  diffuse  readily,  and  are  thus  quickly  absorbed. 

After  entering  the  blood  the  peptones  are  very  soon  again  modified, 
so  as  to  re-assume  the  chemical  characters  of  albumin,  a  change  as  neces- 
sary for  preventing 'their  diffusing  out  of  the  blood-vessels,  as  the  previous 
change  was  for  enabling  them  to  pass  in.  This  is  effected,  probably,  in 
great  part  by  the  agency  of  the  liver. 

Products  of  Gastric  Digestion.— The  chief  product  of  gastric 


248  HAND-BOOK    OF    PHYSIOLOGY. 

digestion  is  undoubtedly  peptone.  We  have  seen,  however,  in  the  above 
experiment  that  there  is  a  by-product,  and  this  is  almost  identical  with 
syntonin  or  acid  albumin.  This  body  is  probably  not  exactly  identical, 
however,  with  syntonin,  and  its  old  name  of  parapeptone  had  better  be 
retained.  The  conversion  of  native  albumin  into  acid  albumin  may  be 
effected 'by  the  hydrochloric  acid  alone,  but  the  further  action  is  undoubt- 
edly due  to  the  ferment  and  the  acid  together,  as  although  under  high 
pressure  any  acid  solution  may,  it  is  said,  if  strong  enough,  produce  the 
entire  conversion  into  peptone,  under  the  condition  of  digestion  in  the 
stomach  this  would  be  quite  impossible;  and,  on  the  other  hand,  pepsin 
will  not  act  without  the  presence  of  acid.  The  production  of  two  forms 
of  peptone  is  usually  recognized,  called  respectively  a^-peptone  and 
^em^-peptone.  Their  differences  in  chemical  properties  have  not  yet  been 
made  out,  but  they  are  distinguished  by  this  remarkable  fact,  that  the 
pancreatic  juice,  while  possessing  no  action  over  the  former,  is  able  to 
convert  the  latter  into  leucin  and  ty rosin.  Pepsin  acts  the  part  of  a 
hydrolytic  ferment  (proteolytic),  and  appears  to  cause  hydration  of  albu- 
min, peptone  being  a  highly  hydrated  form  of  albumin. 

Circumstances  favoring  Gastric  Digestion. — 1.  A  temperature 
of  about  100°  F.  (37 '8°  C.);  at  32°  F.  (0°  C.)  it  is  delayed,  and  by  boil- 
ing is  altogether  stopped.  2.  An  acid  medium  is  necessary.  Hydro- 
chloric is  the  best  acid  for  the  purpose.  Excess  of  acid  or  neutralization 
stops  the  process.  3.  The  removal  of  the  products  of  digestion.  Excess 
of  peptone  delays  the  action. 

Action  of  the  Gastric  Juice  on  Bodies  other  than  Proteids. 
— All  proteids  are  converted  by  the  gastric  juice  into  peptones,  and,  there- 
fore, whether  they  be  taken  into  the  body  in  meat,  eggs,  milk,  bread,  or 
other  foods,  the  resultant  still  is  peptone. 

Milk  is  curdled,  the  casein  being  precipitated,  and  then  dissolved. 
The  curdling  is  due  to  a  special  ferment  of  the  gastric  juice  (curdling 
ferment),  and  is  not  due  to  the  action  of  the  free  acid  only.  The  effect 
of  rennet,  which  is  a  decoction  of  the  fourth  stomach  of  a  calf  in  brine, 
has  long  been  known,  as  it  is  used  extensively  to  cause  precipitation  of 
casein  in  cheese  manufacture. 

The  ferment  which  produces  this  curdling  action  is  distinct  from 
pepsin. 

Gelatin  is  dissolved  and  changed  into  peptone,  as  are  also  cliondrin 
and  elastin;  but  mucin,  and  the  horny  tissues,  keratin  generally  are  un- 
affected. 

On  the  amylaceous  articles  of  food,  and  upon  pure  oleaginous  prin- 
ciples the  gastric  juice  has  no  action.  In  the  case  of  adipose  tissue,  its 
effect  is  to  dissolve  the  areolar  tissue,  albuminous  cell-walls,  etc.,  which 
enter  into  its  composition,  by  which  means  the  fat  is  able  to  mingle 
more  uniformly  with  the  other  constituents  of  the  chyme. 


DIGESTION.  249 

The  gastric  fluid  acts  as  a  general  solvent  for  some  of  the  saline  con- 
stituents of  the  food,  as,  for  example,  particles  of  common  salt,  which 
may  happen  to  have  escaped  solution  in  the  saliva;  while  its  acid  may 
enable  it  to  dissolve  some  other  salts  which  are  insoluble  in  the  latter  or 
in  water.  It  also  dissolves  cane  sugar,  and  by  the  aid  of  its  mucus  causes 
its  conversion  in  part  into  grape  sugar. 

The  action  of  the  gastric  juice  in  preventing  and  checking  putrefac- 
tion has  been  often  directly  demonstrated.  Indeed,  that  the  secretions 
which  the  food  meets  with  in  the  alimentary  canal  are  antiseptic  in  their 
action,  is  what  might  be  anticipated,  not  only  from  the  pronenessio  de- 
composition of  organic  matters,  such  as  those  used  as  food,  especially 
under  the  influence  of  warmth  and  moisture,  but  also  from  the  well- 
known  fact  that  decomposing  flesh  (e.g.,  high  game)  may  be  eaten  with 
impunity,  while  it  would  certainly  cause  disease  were  it  allowed  to  enter 
the  blood  by  any  other  route  than  that  formed  by  the  organs  of  digestion. 

Time  occupied  in  Gastric  Digestion. — Under  ordinary  condi- 
tions, from  three  to  four  hours  may  be  taken  as  the  average  time  occupied 
by  the  digestion  of  a  meal  in  the  stomach.  But  many  circumstances  will 
modify  the  rate  of  gastric  digestion.  The  chief  are:  the  nature  of  the 
food  taken  and  its  quantity  (the  stomach  should  be  fairly  filled — not  dis- 
tended); the  time  that  has  elapsed  since  the  last  meal,  which  should  be 
at  least  enough  for  the  stomach  to  be  quite  clear  of  food;  the  amount  of 
exercise  previous  and  subsequent  to  a  ineal  (gentle  exercise  being  favor- 
able, over-exertion  injurious  to  digestion);  the  state  of  mind  (tranquillity 
of  temper  being  essential,  in  most  cases,  to  a  quick  and  due  digestion); 
the  bodily  health;  and  some  others. 

Movements  of  the  Stomach. — The  gastric  fluid  is  assisted  in 
accomplishing  its  share  in  digestion  by  the  movements  of  the  stomach. 
In  granivorous  birds,  for  example,  the  contraction  of  the  strong  muscular 
gizzard  affords  a  necessary  aid  to  digestion,  by  grinding  and  triturating 
the  hard  seeds  which  constitute  part  of  the  food.  But  in  the  stomachs  of 
man  and  other  Mammalia  the  motions  of  the  muscular  coat  are  too  feeble 
to  exercise  any  such  mechanical  force  on  the  food;  neither  are  they 
needed,  'for  mastication  has  already  done  the  mechanical  work  of  a  giz- 
zard; and  experiments  have  demonstrated  that  substances  enclosed  in 
perforated  tubes,  and  consequently  protected  from  mechanical  influence, 
are  yet  digested. 

The  normal  actions  of  the  muscular  fibres  of  the  human  stomach 
appear  to  have  a  threefold  purpose;  (1)  to  adapt  the  stomach  to  the 
quantity  of  food  in  it,  so  that  its  walls  may  be  in  contact  with  the  food 
on  all  sides,  and,  at  the  same  time,  may  exercise  a  certain  amount  of 
compression  upon  it;  (2)  to  keep  the  orifices  of  the  stomach  closed  until 
the  food  is  digested;  and  (3)  to  perform  certain  peristaltic  movements, 
whereby  the  food,  as  it  becomes  chymified,  is  gradually  propelled  toward, 


250  HAND-BOOK    OF    PHYSIOLOGY. 

and  ultimately  through,  the  pylorus.  In  accomplishing  this  latter  end, 
the  movements  without  doubt  materially  contribute  toward  effecting  a 
thorough  intermingling  of  the  food  and  the  gastric  fluid. 

When  digestion  is  not  going  on,  the  stomach  is  uniformly  contracted, 
its  orifices  not  more  firmly  than  the  rest  of  its  walls;  but,  if  examined 
shortly  after  the  introduction  of  food,  it  is  found  closely  encircling  its 
contents,  and  its  orifices  are  firmly  closed  like  sphincters.  The  cardiac 
orifice,  every  time  food  is  swallowed,  opens  to  admit  its  passage  to  the 
stomach,  and  immediately  again  closes.  The  pyloric  orifice,  during  the 
first  part  of  gastric  digestion,  is  usually  so  completely  closed,  that  even 
when  the  stomach  is  separated  from  the  intestines,  none  of  its  contents 
escape.  But  toward  the  termination  of  the  digestive  process,  the  pylorus 
seems  to  oifer  less  resistance  to  the  passage  of  substances  from  the 
stomach;  first  it  yields  to  allow  the  successively  digested  portions  to  go 
through  it;  and  then  it  allows  the  transit  of  even  undigested  substances. 
It  appears  that  food,  so  soon  as  it  enters  the  stomach,  is  subjected  to  a 
kind  of  peristaltic  action  of  the  muscular  coat,  whereby  the  digested  por- 
tions are  gradually  moved  toward  the  pylorus.  The  movements  were 
observed  to  increase  in  rapidity  as  the  process  of  chymification  advanced, 
and  were  continued  until  it  was  completed. 

The  contraction  of  the  fibres  situated  toward  the  pyloric  end  of  the 
stomach  seems  to  be  more  energetic  and  more  decidedly  peristaltic  than 
those  of  the  cardiac  portion.  Thus,  it  was  found  in  the  case  of  St. 
Martin,  that  when  the  bulb  of  the  thermometer  was  placed  about  three 
inches  from  the  pylorus,  through  the  gastric  fistula,  it  was  tightly  em- 
braced from  time  to  time,  and  drawn  toward  the  pyloric  orifice  for  a  dis- 
tance of  three  or  four  inches.  The  object  of  this  movement  appears  to 
be,  as  just  said,  to  carry  the  food  toward  the  pylorus  as  fast  as  it  is  formed 
into  chyme,  and  to  propel  the  chyme  into  the  duodenum;  the  undigested 
portions  of  food  being  kept  back  until  they  are  also  reduced  into  chyme, 
or  until  all  that  is  digestible  has  passed  out.  The  action  of  these  fibres 
is  often  seen  in  the  contracted  state  of  the  pyloric  portion  of  the  stomach 
after  death,  when  it  alone  is  contracted  and  firm,  while  the  cardiac  por- 
tion forms  a  dilated  sac.  Sometimes,  by  a  predominant  action  of  strong 
circular  fibres  placed  between  the  cardia  and  pylorus,  the  two  portions, 
or  ends  as  they  are  called,  of  the  stomach,  are  partially  separated  from 
each  other  by  a  kind  of  hour-glass  contraction.  By  means  of  the  peri- 
staltic action  of  the  muscular  coats  of  the  stomach,  not  merely  is  chymified 
food  gradually  propelled  through  the  pylorus,  but  a  kind  of  double  cur- 
rent is  continually  kept  up  among  the  contents  of  the  stomach,  the  cir- 
cumferential parts  of  the  mass  being  gradually  moved  onward  toward  the 
pylorus  by  the  contraction  of  the  muscular  fibres,  while  the  central  por- 
tions are  propelled  in  the  opposite  direction,  namely,  toward  the  cardiac 
orifice;  in  this  way  is  kept  up  a  constant  circulation  of  the  contents  of 


DIGESTION.  251 

the  viscus,  highly  conducive  to  their  free  mixture  with  the  gastric  fluid 
and  to  their  ready  digestion. 

Vomiting. — The  expulsion  of  the  contents  of  the  stomach  in  vomit- 
ing, like  that  of  mucous  or  other  matter  from  the  lungs  in  coughing,  is 
preceded  by  an  inspiration;  the  glottis  is  then  closed,  and  immediately 
afterward  the  abdominal  muscles  strongly  act;  but  here  occurs  the  dif- 
ference in  the  two  actions.  Instead  of  the  vocal  cords  yielding  to  the 
action  of  the  abdominal  muscles,  they  remain  tightly  closed.  Thus  the 
diaphragm  being  unable  to  go  up,  forms  an  unyielding  surface  against 
which  the  stomach  can  be  pressed.  In  this  way,  as  well  as  by  its  own 
contraction,  it  is  fixed,  to  use  a  technical  phrase.  At  the  same  time  the 
cardiac  sphincter-muscle  being  relaxed,  and  the  orifice  which  it  naturally 
guards  being  actively  dilated,  while  the  pylorus  is  closed,  and  the  stomach 
itself  also  contracting,  the  action  of  the  abdominal  muscles,  by  these 
means  assisted,  expels  the  contents  of  the  organ  through  the  oesophagus, 
pharynx,  and  mouth.  The  reversed  peristaltic  action  of  the  oesophagus 
probably  increases  the  effect. 

It  has  been  frequently  stated  that  the  stomach  itself  is  quite  passive 
during  vomiting,  and  that  the  expulsion  of  its  contents  is  effected  solely 
by  the  pressure  exerted  upon  it  when  the  capacity  of  the  abdomen  is 
diminished  by  the  contraction  of  the  diaphragm,  and  subsequently  of  the 
abdominal  muscles.  The  experiments  and  observations,  however,  which 
are  supposed  to  confirm  this  statement,  only  show  that  the  contraction  of 
the  abdominal  muscles  alone  is  sufficient  to  expel  matters  from  an  unre- 
sisting bag  through  the  ossophagus;  and  that,  under  very  abnormal 
circumstances,  the  stomach,  by  itself,  cannot  expel  its  contents.  They  by 
no  means  show  that  in  ordinary  vomiting  the  stomach  is  passive;  and, 
on  the  other  hand,  there  are  good  reasons  for  believing  the  contrary. 

It  is  true  that  facts  are  wanting  to  demonstrate  with  certainty  this 
action  of  the  stomach  in  vomiting;  but  some  of  the  cases  of  fistulous  open- 
ing into  the  organ  appear  to  support  the  belief  that  it  does  take  place; 
and  the  analogy  of  the  case  of  the  stomach  with  that  of  the  other  hollow 
viscera,  as  the  rectum  and  bladder,  may  be  also  cited  in  confirmation. 

The  muscles  concerned  in  the  act  of  vomiting,  are  chiefly  and  pri- 
marily those  of  the  abdomen;  the  diaphragm  also  acts,  but  usually  not  as 
the  muscles  of  the  abdominal  walls  do.  They  contract  and  compress  the 
stomach  more  and  more  toward  the  diaphragm;  and  the  diaphragm 
(which  is  usually  drawn  down  in  the  deep  inspiration  that  precedes  each 
act  of  vomiting)  is  fixed,  and  presents  an  unyielding  surface  against 
which  the  stomach  may  be  pressed.  The  diaphragm  is,  therefore,  as  a 
rule,  passive  during  the  actual  expulsion  of  the  contents  of  the  stomach. 
But  there  are  grounds  for  believing  that  sometimes  this  muscle 
actively  contracts,  so  that  the  stomach  is,  so  to  speak,  squeezed  between 
the  descending  diaphragm  and  the  retracting  abdominal  walls. 


252  HAND-BOOK    OF    PHYSIOLOGY. 

Some  persons  possess  the  power  of  vomiting  at  will,  without  applying 
any  undue  irritation  to  the  stomach,  but  simply  by  a  voluntary  effort, 
It  seems  also,  that  this  power  may  be  acquired  by  those  who  do  not 
naturally  possess  it,  and  by  continual  practice  may  become  a  habit.  There 
are  cases  also  of  rare  occurrence  in  which  persons  habitually  swallow  their 
food  hastily,  and  nearly  unmasticated,  and  then  at  their  leisure  regurgi- 
tate it,  piece  by  piece,  into  their  mouth,  remasticate,  and  again  swallow 
it,  like  members  of  the  ruminant  order  of  Mammalia. 

The  various  nerve-actions  concerned  in  vomiting  are  governed  by  a 
nerve-centre  situate  in  the  medulla  oblongata. 

The  sensory  nerves  are  the  fifth,  glosso-pharyngeal  and  vagus  princi- 
pally; but,  as  well,  vomiting  may  occur  from  stimulation  of  sensory 
nerves  from  many  organs,  e.g. ,  kidney,  testicle,  etc.  The  centre  may  also 
be  stimulated  by  impressions  from  the  cerebrum  and  cerebellum,  so  called 
central  vomiting  occurring  in  disease  of  those  parts.  The  eiferent  im- 
pulses are  carried  by  the  phrenics  and  the  spinal  nerves. 

Influence  of  the  Nervous  System  on  Gastric  Digestion. — The 
normal  movements  of  the  stomach  during  gastric  digestion  are  directly 
connected  with  the  plexus  of  nerves  and  ganglia  contained  in  its  walls, 
the  presence  of  food  acting  as  a  stimulus  which  is  conveyed  to  the  gan- 
glia and  reflected  to  the  muscular  fibres.  The  stomach  is,  however,  also 
directly  connected  with  the  higher  nerve-centres  by  means  of  branches 
of  the  vagus  and  solar  plexus  of  the  sympathetic.  The  vaso-motor  fibres 
of  the  latter  are  derived,  probably,  from  the  splanchnic  nerves. 

The  exact  function  of  the  vagi  in  connection  with  the  movements  of 
the  stomach  is  not  certainly  known.  Irritation  of  the  vagi  produces  con- 
traction of  the  stomach,  if  digestion  is  proceeding;  while,  on  the  other 
hand,  peristaltic  action  is  retarded  or  stopped,  when  these  nerves  are 
divided. 

Bernard,  watching  the  act  of  gastric  digestion  in  dogs  which  had  fis- 
tulous  openings  into  their  stomachs,  saw  that  on  the  instant  of  dividing 
their  vagic  nerves,  the  process  of  digestion  was  stopped,  and  the  mucous 
membrane  of  the  stomach,  previously  turgid  with  blood,  became  pale, 
and  ceased  to  secrete.  These  facts  may  be  explained  by  the  theory  that 
the  vagi  are  the  media  by  which,  during  digestion,  an  inhibitory  impulse 
is  conducted  to  the  vaso-motor  centre  in  the  medulla;  such  impulse  being 
reflected  along  the  splanchnic  nerves  to  the  blood-vessels  of  the  stomach, 
and  causing  their  dilatation  (Rutherford).  From  other  experiments  it  may 
be  gathered,  that  although  division  of  both  vagi  always  temporarily  sus- 
pends the  secretion  of  gastric  fluid,  and  so  arrests  the  process  of  digestion, 
being  occasionally  followed  by  death  from  inanition;  yet  the  digestive 
powers  of  the  stomach  may  be  completely  restored  after  the  operation, 
and  the  formation  of  chyme  and  the  nutrition  of  the  animal  may  be 
carried  on  almost  as  perfectly  as  in  health.  This  would  indicate  the 


DIGESTION. 


253 


existence  of  a  special  local  nervous  mechanism  which  controls  the 
secretion. 

Bernard  found  that  galvanic  stimulus  of  these  nerves  excited  an  active 
secretion  of  "the  fluid,  while  a  like  stimulus  applied  to  the  sympathetic 
nerves  issuing  from  the  semilunar  ganglia,  caused  a  diminution  and  even 
complete  arrest  of  the  secretion. 

The  influence  of  the  higher  nerve-centres  on  gastric  digestion,  as  in 
the  case  of  mental  emotion,  is  too  well  known  to  need  more  than  a  ref- 
erence. 

Digestion  of  the  Stomach  after  Death. — If  an  animal  die  dur- 
ing the  process  of  gastric  digestion,  and  when,  therefore,  a  quantity  of 
gastric  juice  is  present  in  the  interior  of  the  stomach,  the  walls  of  this 
organ  itself  are  frequently  themselves  acted  on  by  their  own  secretion, 
and  to  such  an  extent,  that  a  perforation  of  considerable  size  may  be  pro- 
duced, and  the  contents  of  the  stomach  may  in  part  escape  into  the 
cavity  of  the  abdomen.  This  phenomenon  is  not  unfrequently  observed 
in  post-mortem  examinations  of  the  human  body.  If  a  rabbit  be  killed 
during  a  period  of  digestion,  and  afterward  exposed  to  artificial  warmth 
to  prevent  its  temperature  from  falling,  not  only  the  stomach,  but  many 
of  the  surrounding  parts,  will  be  found  to  have  been  dissolved  (Pavy). 

From  these  facts,  it  becomes  an  interesting  question  why,  during  life, 
the  stomach  is  free  from  liability  to  injury  from  a  secretion  which,  after 
death,  is  capable  of  such  destructive  eifects? 

It  is  only  necessary  to  refer  to  the  idea  of  Bernard,  that  the  living 
stomach  finds  protection  from  its  secretion  in  the  presence  of  epithelium 
and  mucus,  which  are  constantly  renewed  in  the  same  degree  that  they 
are  constantly  dissolved,  in  order  to  remark  that,  although  the  gastric 
mucus  is  probably  protective,  this  theory,  so  far  as  the  epithelium  is  con- 
cerned, has  been  disproved  by  experiments  of  Pavy's,  in  which  the  mucous 
membrane  of  the  stomachs  of  dogs  was  dissected  off  for  a  small  space, 
and,  on  killing  the  animals  some  days  afterward,  no  sign  of  digestion  of 
the  stomach  was  visible.  '"Upon  one  occasion,  after  removing  the  mu- 
cous membrane,  and  exposing  the  muscular  fibres  over  a  space  of  about  an 
inch  and  a  half  in  diameter,  the  animal  was  allowed  to  live  for  ten  days. 
It  ate  food  every  day,  and  seemed  scarcely  affected  by  the  operation.  Life 
was  destroyed  whilst  digestion  was  being  carried  on,  and  the  lesion  in  the 
stomach  was  found  very  nearly  repaired:  new  matter  had  been  deposited 
in  the  place  of  what  had  been  removed,  and  the  denuded  spot  had  con- 
tracted to  much  less  than  its  original  dimensions." 

Pavy  believes  that  the  natural  alkalinity  of  the  blood,  which  circulates 
so  freely  during  life  in  the  walls  of  the  stomach,  is  sufficient  to  neutralize 
the  acidity  of  the  gastric  juice;  and  as  may  be  gathered  from  what  has 
been  previously  said,  the  neutralization  of  the  acidity  of  the  gastric  secre- 
tion is  quite  sufficient  to  destroy  its  digestive  powers;  but  the  experi- 


254  HAND-BOOK    OF    PHYSIOLOGY. 

ments  adduced  in  favor  of  this  theory  are  open  to  many  objections,,  and 
afford  only  a  negative  support  to  the  conclusions  they  are  intended  to 
prove.  Again,  the  pancreatic  secretion  acts  best  on  proteids  in  an  alka- 


FIG.  181.— Auerbach's  nerve-plexus  in  small  intestine.  The  plexus  consists  of  fibrillated  substance, 
and  is  made  up  of  trabeculae  of  various  thicknesses.  Nucleus-like  elements  and  ganglion-cells  are  im- 
bedded in  the  plexus,  the  whole  of  which  is  enclosed  in  a  nucleated  sheath.  (Klein.) 

line  medium;  but  it  has  no  digestive  action  on  the  living  intestine.     It 
must  be  confessed  that  no  entirely  satisfactory  theory  has  been  yet  stated. 

THE  INTESTINES. 

The  Intestinal  Canal  is  divided  into  two  chief  portions,  named  from 
their  differences  in  diameter,  the  (I.)  small  and  (II.)  large  intestine  (Fig. 
165).  These  are  continuous  with  each  other,  and  communicate  by  means 
of  an  opening  guarded  by  a  valve,  the  ileo-ccecal  valve,  which  allows  the 
passage  of  the  products  of  digestion  from  the  small  into  the  large  bowel, 
but  not,  under  ordinary  circumstances,  in  the  opposite  direction. 

/.  The  Small  Intestine. — The  Small  Intestine,  the  average  length  of 
which  in  an  adult  is  about  twenty  feet,  has  been  divided,  for  convenience 
of  description,  into  three  portions,  viz.,  the  duodenum,  which  extends  for 
eight  or  ten  inches  beyond  the  pylorus;  the  jejunum,  which  forms  two- 
fifths,  and  the  ileum,  which  forms  three-fifths  of  the  rest  of  the  canal. 

Structure. — The  small  intestine,  like  the  stomach,  is  constructed  of 
four  principal  coats,  viz.,  the  serous,  muscular,  submucous,  and  mucous. 

(1)  The  serous  coat,  formed  by  the  visceral  layer  of  the  peritoneum, 
and  has  the  structure  of  serous  membranes  in  general. 

(2)  The  muscular  coats  consist  of  an  internal  circular  and  an  external 
longitudinal  layer:  the  former  is  usually  considerably  the  thicker.     Both 


DIGESTION. 


255 


alike  consist  of  bundles  of  unstriped  muscular  tissue  supported  by  con- 
nective tissue.  They  are  well  provided  with  lymphatic  vessels,  which 
form  a  set  distinct  from  those  of  the  mucous  membrane. 

Between  the  two  muscular  coats  is  a  nerve-plexus  (Auerbach's  plexus, 
plexos  myentericus)  (Pig.  181)  similar  in  structure  to  Meissner's  (in  the 
submucous  tissue),  but  with  more  numerous  ganglia.  This  plexus  regu- 
lates the  peristaltic  movements  of  the  muscular  coats  of  the  intestines. 

(3)  Between  the  mucous  and  muscular  coats,  is  the  submucous  coat, 
which  consists  of  connective  tissue,  in  which  numerous  blood-vessels  and 
lymphatics  ramify.  A  fine  plexus,  consisting  mainly  of  non-medullated 
nerve-fibres,  "Meissner's  plexus,"  with  ganglion  cells  at  its  nodes,  occurs 


FIG.  182.— Horizontal  section  of  a  small  fragment  of  the  mucous  membrane,  including  one  entire 
crypt  of  Lieberkuhn  and  parts  of  several  others:  a,  cavity  of  the  tubular  glands  or  crypts;  6,  one 
of  the  lining  epithelial  cells;  c,  the  lymphoid  or  retiform  spaces,  of  which  some  are  empty,  and  others 
occupied  by  lymph  cells,  as  at  d. 

in  the  submucous  tissue  from  the  stomach  to  the  anus.  From  the  posi- 
tion of  this  plexus  and  the  distribution  of  its  branches,  it  seems  highly 
probable  that  it  is  the  local  centre  for  regulating  the  calibre  of  the  blood- 
vessels supplying  the  intestinal  mucous  membrane,  and  presiding  over  the 
processes  of  secretion  and  absorption. 

(4)  The  mucous  membrane  is  the  most  important  coat  in  relation  to 
the  function  of  digestion.  The  following  structures,  which  enter  into  its 
composition,  may  now  be  successively  described; — the  valvulce  conniventes; 
the  vitti;  and  the  glands.  The  general  structure  of  the  mucous  mem- 
brane of  the  intestines  resembles  that  of  the  stomach  (p.  241),  and,  like 
it,  is  lined  on  its  inner  surface  by  columnar  epithelium.  Adenoid  tissue 
(Fig.  182,  c  and  d)  enters  largely  into  its  construction;  and  on  its  deep 
surface  is  the  muscularis  mucosce  (m  m,  Fig.  183),  the  fibres  of  which  are 
arranged  in  two  layers:  the  outer  longitudinal  and  the  inner  circular. 

Valvulae  Conniventes. — The  valvulce  conniventes  (Fig.  184)  com- 
mence in  the  duodenum,  about  one  or  two  inches  beyond  the  pylorus,  and 
becoming  larger  and  more  numerous  immediately  beyond  the  entrance  of 
the  bile  duct,  continue  thickly  arranged  and  well  developed  throughout 


256 


HAND-BOOK    OF    PHYSIOLOGY. 


the  jejunum;  then,  gradually  diminishing  in  size  and  number,  they  cease 
near  the  middle  of  the  ileum.  They  are  formed  by  a  doubling  inward  of 
the  mucous  membrane;  the  crescentic,  nearly  circular,  folds  thus  formed 
being  arranged  transversely  to  the  axis  of  the  intestine,  and  each  indi- 
vidual fold  seldom  extending  around  more  than  ^  or  f  of  the  bowel's  cir- 
cumference. Unlike  the  rugae  in  the  oesophagus  and  stomach,  they  do 
not  disappear  on  distension  of  the  canal.  Only  an  imperfect  notion  of 
their  natural  position  and  function  can  be*  obtained  by  looking  at  them 
after  the  intestine  has  been  laid  open  in  the  usual  manner.  To  under- 


X.Tfl, 


FIG.  183. 


FIG.  184. 


FIG.  183.— Vertical  section  Arough  portion  of  small  intestine  of  dog.  v,  two  villi  showing  e,  epithe- 
i;  (/,  goblet  cells.    The  free  surface  is  seen  to  be  formed  by  the  "striated  basilar  border, "  while 


FIG. 
lium ; 

inside  the  villus  the  adenoid  tissue  and  unstriped  muscle-cells  are  seen ;  If,  Lieberkuhn's  follicles :  m 
m,  muscularis  mucosee,  sending  up  fibres  between  the  follicles  into  the  villi;  sm,  submucous  tissue; 
containing  (gm),  ganglion  cells  of  Meissner's  plexus.  (Schofield.) 

FIG.  184.— Piece  of  small  intestine  (previously  distended  and  hardened  by  alcohol)  laid  open  to 
show  the  normal  position  of  the  valvulea  conniventes. 


stand  them  aright,  a  piece  of  gut  should  be  distended  either  with  air  or 
alcohol,  and  not  opened  until  the  tissues  have  become  hardened.  On 
then  making  a  section  it  will  be  seen  that,  instead  of  disappearing,  they 
stand  out  at  right  angles  to  the  general  surface  of  the  mucous  membrane 
(Fig.  184).  Their  functions  are  probably  less — Besides  (1)  offering  a 
largely  increased  surface  for  secretion  and  absorption,  they  probably  (2) 
prevent  the  too  rapid  passage  of  the  very  liquid  products  of  gastric  diges- 
tion, immediately  after  their  escape  from  the  stomach,  and  (3),  by  their 
projection,  and  consequent  interference  with  a  uniform  and  untroubled 
current  of  the  intestinal  contents,  "probably  assist  in  the  more  p'erfect 
mingling  of  the  latter  with  the  secretions  poured  out  to  act  on  them. 


DIGESTION. 


257 


Glands  of  the  Small  Intestine.— The  glands  are  of  three  princi- 
pal kinds:— viz.,  those  of  (1)  Lieberkuhn,  (2)  Brunner,  and  (3)  Peyer. 

(1.)  The  glands  or  crypts  of  Lieberkuhn  are  simple  tubular  depressions 
of  the  intestinal  mucous  membrane,  thickly  distributed  over  the  whole  sur- 
face both  of  the  large  and  small  intestines.  In  the  small  intestine  they 
are  visible  only  with  the  aid  of  a  lens;  and  their  orifices  appear  as  minute 
dots  scattered  between  the  villi.  They  are  larger  in  the  large  intestine, 
and  increase  in  size  the  nearer  J:hey  approach  the  anal  end  of  the  intes- 
tinal tube;  and  in  the  rectum  their  orifices  may  be  visible  to  the  naked 
eye.  In  length  they  vary  from  -^  to  -fa  of  a  line.  Each  tubule  (Fig. 
186)  is  constructed  of  the  same  essential  parts  as  the  intestinal  mucous 
membrane,  viz.,  a.  fine  membrana  propria,  or  basement  membrane,  a 


FIG.  185. 


FIG.  186. 


FIG.  185.  —  Transverse  section  through  four  crypts  of  Lieberkuhn  from  the  large  intestine  of  the 


pig.    They  are  lined  by  columnar  epithelial  cells,  the  nuclei  being  placed  in  the  outer  part  of  the 
cells.    The  divisions  between  the  cells  are  seen  as  lines  radiating 
epithelial  cells,  which  have  become  transformed  into  goblet  cells, 


FIG.  186.—  A  gland  of  Lieberkuhn  in  longitudinal  section. 


from  L,  the  lumen  of  the  crypt;  G, 
x  350.    (Klein  and  Noble  Smith.) 
(Brinton.) 


layer  of  cylindrical  epithelium  lining  it,  and  capillary  blood-vessels  cover- 
ing its  exterior,  the  free  surface  of  the  columnar  cells  presenting  an 
appearance  precisely  similar  to  the  "striated  basilar  border"  which  covers 
the  villi.  Their  contents  appear  to  vary,  even  in  health;  the  varieties 
being  dependent,  probably,  on  the  period  of  time  in  relation  to  digestion 
at  which  they  are  examined. 

Among  the  columnar  cells  of  Lieberkuhn's  follicles,  goblet-cells  fre- 
quently occur  (Fig.  185). 

(2.)  Brunner'  s  glands  (Fig.  188)  are  confined  to  the  duodenum;  they 
are  most  abundant  and  thickly  set  at  the  commencement  of  this  portion 
of  the  intestine,  diminishing  gradually  as  the  duodenum  advances.  They 
are  situated  beneath  the  mucous  membrane,  and  imbedded  in  the  submu- 
cous  tissue,  each  gland  is  a  branched  and  convoluted  tube,  lined  with 
columnar  epithelium.  As  before  said,  in  structure  they  are  very  similar 
to  the  pyloric  glands  of  the  stomach,  and  their  epithelium  undergoes  a 
VOL.  I.—  17. 


258 


HAND-BOOK    OF    PHYSIOLOGY. 


similar  change  during  secretion;  but 'they  are  more  branched  and  convo- 
luted and  their  ducts  are  longer.  (Watney.)  The  duct  of  each  gland 
passes  through  the  muscularis  mucosse,  and  opens  on  the  surface  of  the 
mucous  membrane. 

(3.)  The  glands  of  Peyer  occur  chiefly  but  not  exclusively  in  the  small 
intestine.     They  are  found  in  greatest  abundance  in  the  lower  part  of  the 


FIG.  187. 


FIG.  188. 


FIG.  187.— Transverse  section  of  injected  Peyer's  glands  (from  Kolliker).  The  drawing  was  taken 
from  a  preparation  made  by  Frey:  it  represents  the  fine  capillary-looped  network  spreading  from 
the  surrounding  blood-vessels  into  the  interior  of  three  of  Peyser's  capsules  from  the  intestine  of  the 
rabbit. 

FIG.  188.— Vertical  section  of  duodenum,  showing  a,  yilli;  b,  crypts  of  Lieberkuhn,  and  c,  Brun- 
ner's  glands  in  the  submucosa  s,  with  ducts,  d:  muscularis  mucosae,  m;  and  circular  muscular  coat/. 
(Schofield.) 

ileum  near  to  the  ileo-caecal  valve.  They  are  met  with  in  two  conditions, 
viz.,  either  scattered  singly,  in  which  case  they  are  termed  glandules  soli- 
tarice,  or  aggregated  in  groups  varying  from  one  to  three  inches  in  length 
and  about  half-an-inch  in  width,  chiefly  of  an  oval  form,  their  long  axis 
parallel  with  that  of  the  intestine.  In  this  state, they  are  named  glandules 
agminate,  the  groups  being  commonly  called  Peyer's  patches  (Fig.  189), 
and  almost  always  placed  opposite  the  attachment  of  the  mesentery.  In 
structure,  and  in  function,  there  is  no  essential  difference  between  the 
solitary  glands  and  the  individual  bodies  of  which  each  group  or  patch  is 
made  up.  They  are  really  single  or  aggregated  masses  of  adenoid  tissue 


DIGESTION.  259 

forming  lymph-follicles.  In  the  condition  in  which  they  have  been  most 
commonly  examined,  each  gland  appears  as  a  circular  opaque-white 
rounded  body,  from  ^  to  -^  inch  in  diameter,  according  to  the  degree  in 
which  it  is  developed.  They  are  principally  contained  in  the  submucous 
coat,  but  sometimes  project  through  the  muscularis  mucosce  into  the 
"mucous  membrane.  In  the  agminate  glands,  each  follicle  reaches  the 
free  surface  of  the  intestine,  and  is  covered  with  columnar  epithelium. 
Each  gland  is  surrounded  by  the  openings  of  Lieberkuhn's  follicles. 

The  adjacent  glands  of  a  Peyer's  patch  are  connected  together  by  ade- 
noid tissue.  Sometimes  the  lymphoid  tissue  reaches  the  free  surface, 
replacing  the  epithelium,  as  is  also  the  case  with  some  of  the  lymphoid 
follicles  of  the  tonsil  (p.  236). 

Fever's  glands  are  surrounded  by  lymphatic  sinuses  which  do  not 
penetrate  into  their  interior;  the  interior  is,  however,  traversed  by  a  very 
rich  blood  capillary  plexus.  If  the  vermiform  appendix  of  a  rabbit,  which 
consists  largely  of  Peyer's  glands,  be  injected  with  blue,  by  pressing  the 


FIG.  189.— Agminate  follicles,  or  Peyer's  patch,  in  a  state  of  distension,    x  5.    (Boehm.) 

point  of  a  fine  syringe  into  one  of  the  lymphatic  sinuses,  the  Peyer's 
glands  will  appear  as  greyish  white  spaces  surrounded  by  blue;  if  now  the 
arteries  of  the  same  be  injected  with  red,  the  greyish  patches  will  change 
to  red,  thus  proving  that  they  are  surrounded  by  lymphatic  spaces,  but 
penetrated  by  blood-vessels.  The  lacteals  passing  out  of  the  villi  commu- 
nicate with  the  lymph  sinuses  round  Peyer's  glands. 

It  is  to  be  noted  that  they  are  largest  and  most  prominent  in  children 
and  young  persons. 

Villi.— The  Villi  (Figs.  183,  188,  190,  and  191),  are  confined  exclu- 
sively to  the  mucous  membrane  of  the  small  intestine.  They  are  minute 
vascular  processes,  from  a  quarter  of  a  line  to  a  line  and  two-thirds  in 
length,  covering  the  surface  of  the  mucous  membrane,  and  giving  it  a 
peculiar  velvety,  fleecy  appearance.  Krause  estimates  them  at  fifty  to 
ninety  in  number  in  a  square  line,  at  the  upper  part  of  the  small  intes- 


260  HAND-BOOK    OF    PHYSIOLOGY. 

tine,  and  at  forty  to  seventy  in  the  same  area  at  the  lower  part.  They 
vary  in  form  even  in  the  same  animal,  and  differ  according  as  the  lym- 
phatic vessels  they  contain  are  empty  or  full  of  chyle;  being  usually,  in 
the  former  case,  flat  and  pointed  at  their  summits,  in  the  latter  cylindri- 
cal or  cleavate. 

Each  villus  consists  of  a  small  projection  of  mucous  membrane,  and 
its  interior  is  therefore  supported  throughout  by  fine  adenoid  tissue,  which 
forms  the  framework  or  stroma  in  which  the  other  constituents  are  con- 
tained. 

The  surface  of  the  villus  is  clothed  by  columnar  epithelium,  which 
rests  on  a  fine  basement  membrane;  while  within  this  are-  found,  reckon- 
ing from  without  inward,  blood-vessels,  fibres  of  the  muscularis  mucosce, 
and  a  single  lymphatic  or  lacteal  vessel  rarely  looped  or  branched  (Fig. 
192);  besides  granular  matter,  fat-globules,  etc. 


^ 


'  > 

FIG.  190.  FIG.  191. 

FIG.  190.— Section  of  small  intestine  showing  villi,  Lieberkiihn's  glands  and  a  Peyer's  solitary 
gland,  m,  m,  muscularis  mucosee.  (Klein  and  Noble  Smith.) 

FIG.  191.— Vertical  section  of  a  villus  of  the  small  intestine  of  a  cat.  a,  striated  basilar  border  of 
the  epithelium ;  b,  columnar  epithelium ;  c,  goblet  cells ;  d,  central  lymph-vessel ;  e,  smooth  muscular 
fibres;  /,  adenoid  stroma  of  the  villus  in  which  lymph. corpuscles  lie.  (Klein.) 

The  epithelium-  is  of  the  columnar  kind,  and  continuous  with  that 
lining  the  other  parts  of  the  mucous  membrane.  The  cells  are  arranged 
with  their  long  axis  radiating  from  the  surface  of  the  villus  (Fig.  191), 
and  their  smaller  ends  resting  on  the  basement  membrane.  The  free 
surface  of  the  epithelial  cells  of  the  villi,  like  that  of  the  cells  which  cover 
the  general  surface  of  the  mucous  membrane,  is  covered  by  a  fine  border 
which  exhibits  very  delicate  striations,  whence  it  derives  its  name,  "stria- 
ted basilar  border." 

Beneath  the  basement  or  limiting  membrane  there  is  a  rich  supply  of 
blood-vessels.  Two  or  more  minute  arteries  are  distributed  within  each 
villus;  and  from  their  capillaries,  which  form  a  dense  network,  proceed 
one  or  two  small  veins,  which  pass  out  at  the  base  of  the  villus. 

The  layer  of  the  muscularis  mucosce  in  the  villus  forms  a  kind  of  thin 
hollow  cone  immediately  around  the  central  lacteal,  and  is,  therefore, 


DIGESTION.  261 

situate  beneath  the  blood-vessels.     It  is  without  doubt  instrumental  in 
the  propulsion  of  chyle  along  the  lacteal. 

The  lacteal  vessel  enters  the  base  of  each  villus,  and  passing  up  in  the 
middle  of  it,  extends  nearly  to  the  tip,  where  it  ends  commonly  by  a 
closed  and  somewhat  dilated  extremity.  In  the  larger  villi  there  may  be 
two  small  lacteal  vessels  which  end  by  a  loop  (Fig.  192),  or  the  lacteals 
may  form  a  kind  of  network  in  the  villus.  The  last  method  of  ending, 
however,  is  rarely  or  never  seen  in  the  human  subject,  although  common 
in  some  of  the  lower  animals  (A,  Fig.  192). 


FIG.  192.— A.  Villus  of  sheep.    B.  Villi  of  man.    (Slightly  altered  from  Teichmann.) 

The  office  of  the  villi  is  the  absorption  of  chyle  and  other  liquids  from 
the  intestine.  The  mode  in  which  they  affect  this  will  be  considered  in 
the  Chapter  on  ABSORPTION. 

II.  The  Large  Intestine. — The  Large  Intestine,  which  in  an  adult  is 
from  about  4  to  6  feet  long,  is  subdivided  for  descriptive  purposes  into 
three  portions  (Fig.  165),  viz.: — the  ccecum,  a  short  wide  pouch,  commu- 
nicating with  the  lower  end  of  the  small  intestine  through  an  opening, 
guarded  by  the  ileo-ccecal  valve;  the  colon,  continuous  with  the  caecum, 
which  forms  the  principal  part  of  the  large  intestine,  and  is  divided  into 
an  ascending,  transverse  and  descending  portion;  and  the  rectum,  which, 
after  dilating  at  its  lower  part,  again  contracts,  and  immediately  afterward 


262 


HAND-BOOK    OF    PHYSIOLOGY. 


opens  externally  through  the  anus.     Attached  to  the  caecum  is  the  small 
appendix  vermiformis. 

Structure. — Like  the  small  intestine,  the  large  is  constructed  of  four 
principal  coats,  viz.,  the  serous,  muscular,  submucous,  and  mucous.  The 
serous  coat  need  not  be  here  particularly  described.  Connected  with  it 
are  the  small  processes  of  peritoneum,  containing  fat,  called  appendices 
epiploiccB.  The  fibres  of  the  muscular  coat,  like  those  of  the  small  in- 
testine, are  arranged  in  two  layers — the  outer  longitudinal,  the  inner  circu- 
lar. In  the  caecum  and  colon,  the  longitudinal  fibres,  besides  being,  as 
in  the  small  intestine,  thinly  disposed  in  all  parts  of  the  wall  of  the  bowel, 


FIG.  193.— Diagram  of  lacteal  vessels  in  small  intestine.  A,  lacteals  in  villi ;  p,  Peyer's  glands;  B 
and  D,  superficial  and  deep  network  of  lacteals  in  submucous  tissue;  L,  Lieberkiihn's  glands;  E,  small 
branch  of  lacteal  vessel  on  its  way  to  mesenteric  gland;  H  and  o,  muscular  fibres  of  intestine;  s,  peri- 
toneum. (Teichmann.) 

are  collected,  for  the  most  part,  into  three  strong  bands,  which  being 
shorter,  from  end  to  end,  than  the  other  coats  of  the  intestine,  hold  the 
canal  in  folds,  bounding  intermediate  sacculi.  On  the  division  of  these 
bands,  the  intestine  can  be  drawn  out  to  its  full  length,  and  it  then  as- 
sumes, of  course,  a  uniformly  cylindrical  form.  In  the  rectum,  the  fas- 
ciculi of  these  longitudinal  bands  spread  out  and  mingle  with  the  other 
longitudinal  fibres,  forming  with  them  a  thicker  layer  of  fibres  than  exists 
on  any  other  part  of  the  intestinal  canal.  The  circular  muscular  fibres 
are  spread  over  the  whole  surface  of  the  bowel,  but  are  somewhat  more 


DIGESTION.  263 

marked  in  the  intervals  between  the  sacculi.  Toward  the  lower  end  of 
the  rectum  they  become  more  numerous,  and  at  the  anus  they  form  a 
strong  band  called  the  internal  sphincter  muscle. 

The  mucous  membrane  of  the  large,  like  that  of  the  small  intestine,  is 
lined  throughout  by  columnar  epithelium,  but,  unlike  it,  is  quite  smooth 
and  destitute  of  villi,  and  is  not  projected  in  the  form  of  valvulce  conni- 
ventes.  Its  general  microscopic  structure  resembles  that  of  the  small  in- 
testine: and  it  is  bounded  below  by  the  muscularis  mucosce. 

The  general  arrangement  of  ganglia  and  nerve-fibres  in  the  large  in- 
testine resembles  that  in  the  small  (p.  255). 

Glands  of  the  Large  Intestine. — The  glands  with  which  the 
large  intestine  is  provided  are  of  two  kinds,  (1)  the  tubular  and  (2)  the 
lymphoid. 


FIG.  194.— Horizontal  section  through  a  portion  of  the  mucous  membrane  of  the  large  intestine, 
showing  Lieberktihn's  glands  in  transverse  section,  a,  lumen  of  gland— lining  of  columnar  cells 
with  c,  goblet  cells,  6,  supporting  connective  tissue.  Highly  magnified.  (V.  D.  Harris.) 

(1.)  The  tubular  glands,  or  glands  of  Lieberkiihn,  resemble  those  of 
the  small  intestine,  but  are  somewhat  larger  and  more  numerous.  They 
are  also  more  uniformly  distributed. 

(2.)  Follicles  of  adenoid  or  lymphoid  tissue  are  most  numerous  in  the 
caecum  and  vermiform  appendix.  They  resemble  in  shape  and  structure, 
almost  exactly,  the  solitary  glands  of  the  small  intestine. 

Peyer's  patches  are  not  found  in  the  large  intestine. 

Ileo-Caecal  Valve.— The  ileo-csecal  valve  is  situate  at  the  place  of 
junction  of  the  small  with  the  large  intestine,  and  guards  against  any  re- 
flex of  the  contents  of  the  latter  into  the  ileum.  It  is  composed  of  two 
semilunar  folds  of  mucous  membrane.  Each  fold  is  formed  by  a  doubling 
inward  of  the  mucous  membrane,  and  is  strengthened  on  the  outside  by 


264  HAND-BOOK    OF    PHYSIOLOGY. 

some  of  the  circular  muscular  fibres  of  the  intestine,  which  are  contained 
between  the  cuter  surfaces  of  the  two  layers  of  which  each  fold  is  composed. 
While  the  circular  muscular  fibres,  however,  of  the  bowel  at  the  junction 
of  the  ileum  with  the  caecum  are  contained  between  the  outer  opposed 
surfaces  of  the  folds  of  mucous  membrane  which  form  the  valve,  the 
longitudinal  muscular  fibres  and  the  peritoneum  of  the  small  and  large 
intestine  respectively  are  continuous  with  each  other,  without  dipping 
in  to  follow  the  circular  fibres  and  the  mucous  membrane.  In  this  man- 
ner, therefore,  the  folding  inward  of  these  two  last-named  structures  is 
preserved,  while,  on  the  other  hand,  by  dividing  the  longitudinal  muscu- 
lar fibres  and  the  peritoneum,  the  valve  can  be  made  to  disappear,  just 
as  the  constrictions  between  the  sacculi  of  the  large  intestine  can  be 
made  to  disappear  by  performing  a  similar  operation.  The  inner  surface 
of  the  folds  is  smooth;  the  mucous  membrane  of  the  ileum  being  con- 
tinuous with  that  of  the  caecum.  That  surface  of  each  fold  which  looks 
toward  the  small  intestine  is  covered  with  villi,  while  that  which  looks  to 
the  caecum  has  none.  When  the  caecum  is  distended,  the  margin  of  the 
folds  are  stretched,  and  thus  are  brought  into  firm  apposition  one  with 
the  other. 

DIGESTION  IN  THE  INTESTINES. 

After  the  food  has  been  duly  acted  upon  by  the  stomach,  such  as  has 
not  been  absorbed  passes  into  the  duodenum,  and  is  there  subjected  to 
the  action  of  the  secretions  of  the  pancreas  and  liver,  which  enter  that 
portion  of  the  small  intestine.  Before  considering  the  changes  which 
the  food  undergoes  in  consequence,  attention  should  be  directed  to  the 
structure  and  secretion  of  these  glands,  and  to  the  secretion  (succus  en- 
tericus)  which  is  poured  out  into  the  intestines  from  the  glands  lining 
them. 

THE  PANCBEAS,  AND  ITS  SECKETION. 

The  Pancreas  is  situated  within  the  curve  formed  by  the  duodenum; 
and  its  main  duct  opens  into  that  part  of  the  small  intestine,  through  a 
small  opening,  or  through  a  duct  common  to  it  and  to  the  liver,  about 
two  and  a  half  inches  from  the  pylorus. 

Structure. — In  structure  the  pancreas  bears  some  resemblance  to  the 
salivary  glands.  Its  capsule  and  septa,  as  well  as  the  blood-vessels  and 
lymphatics,  are  similarly  distributed.  It  is,  however,  looser  and  softer, 
the  lobes  and  lobules  being  less  compactly  arranged.  The  main  duct 
divides  into  branches  (lobar  ducts),  one  for  each  lobe,  and  these  branches 
subdivide  into  intralobular  ducts,  and  these  again  by  their  division  and 
branching  form  the  gland  tissue  proper.  The  intralobular  ducts  corre- 


DIGESTION.  265 


spond  to  a  lobule,  while  between  them  and  the  secreting  tubes  or 
are  longer  or  shorter  intermediary  ducts.  The  larger  ducts  possess  a 
very  distinct  lumen  and  a  membrana  propria  lined  with  columnar  epi- 
thelium, the  cells  of  which  are  longitudinally  striated,  but  are  shorter 
than  those  found  in  the  ducts  of  the  salivary  glands.  In  the  intralobular 
ducts  the  epithelium  is  short  and  the  lumen  is  smaller.  The  intermediary 
ducts  opening  into  the  alveoli  possess  a  distinct  lumen,  with  a  membrana 
propria  lined  with  a  single  layer  of  flattened  elongated  cells.  The  alveoli 
arc  branched  and  convoluted  tubes,  with  a  membrana  propria  lined  with 
a  single  layer  of  columnar  cells.  They  have  no  distinct  lumen,  its  place 
being  taken  by  fusiform  or  branched  cells.  Heidenhain  has  observed 
that  the  alveoli  cells  in  the  pancreas  of  a  fasting  dog  consist  of  two  zones, 
an  inner  or  central  zone,  which  is  finely  granular,  and  which  stains  feebly, 


Fro.  195.— Section  of  the  pancreas  of  a  dog  during  digestion,  a,  alveoli  lined  with  cells,  the  outer 
zone  of  which  is  well  stained  with  haematoxylin ;  d,  intermediary  duct  lined  with  squamous  epithelium. 
X  350.  (Klein  and  Noble  Smith.) 

and  a  smaller  parietal  zone  of  finely  striated  protoplasm,  which  stains 
easily.  The  nucleus  is  partly  in  one,  partly  in  the  other  zone.  During 
digestion,  it  is  found  that  the  outer  zone  increases  in  size,  and  the  central 
zone  diminishes;  the  cell  itself  becoming  smaller  from  the  discharge  of 
the  secretion.  At  the  end  of  digestion  the  first  condition  again  appears, 
the  inner  zone  enlarging  at  the  expense  of  the  outer.  It  appears  that  the 
granules  are  formed  by  the  protoplasm  of  the  cells,  from  material  supplied 
to  it  by  the  blood.  The  granules  are  thought  to  be  not  the  ferment 
itself,  but  material  from  which,  under  certain  conditions,  the  ferments  of 
the  gland  are  made,  and  therefore  called  Zymogen. 

Pancreatic  Secretion. — The  secretion  of  the  pancreas  has  been  ob- 
tained for  purposes  of  experiment  from  the  lower  animals,  especially  the 
dog,  by  opening  the  abdomen  and  exposing  the  duct  of  the  gland,  which 
is  then  made  to  communicate  with  the  exterior .  A  pancreatic  fistula  is 
thus  established. 


266  HAND-BOOK    OF    PHYSIOLOGY. 

An  extract  of  pancreas  made  from  the  gland,  which  has  been  removed 
from  an  animal  killed  during  digestion,  possesses  the  active  properties  of 
pancreatic  secretion.  It  is  made  by  first  dehydrating  the  gland,  which 
has  been  cut  up  into  small  pieces,  by  keeping  it  for  some  days  in  absolute 
alcohol,  and  then,  after  the  entire  removal  of  the  alcohol,  placing  it  in 
strong  glycerin.-  A  glycerin  extract  is  thus  obtained.  It  is  a  remarkable 
fact,  however,  that  the  amount  of  the  ferment  trypsin  greatly  increases 
if  the  gland  be  exposed  to  the  air  for  twenty-four  hours  before  placing  in 
alcohol;  indeed,  a  glycerin  extract  made  from  the  gland  immediately 
upon  removal  from  the  body  often  appears  to  contain  none  of  that  fer- 
ment. This  seems  to  indicate  that  the  conversion  of  zymogen  in  the 
gland  into  the  ferment  only  takes  place  during  the  act  of  secretion,  and 
that  the  gland,  although  it  always  contains  in  its  cells  the  materials  (tryp- 
sinogen)  out  of  which  trypsin  is  formed,  yet  the  conversion  of  the  one 
into  the  other  only  takes  place  by  degrees.  Dilute  acid  appears  to  assist 
and  accelerate  the  conversion,  and  if  a  recent  pancreas  be  rubbed  up  with 
dilute  acid  before  dehydration,  a  glycerin  extract  made  afterward,  even 
though  the  gland  may  have  been  only  recently  removed  from  the  body,  is 
very  active. 

Properties. — Pancreatic  juice  is  colorless,  transparent,  and  slightly 
viscid,  alkaline  in  reaction.  It  varies  in  specific  gravity  from  1010  to 
1015,  according  to  whether  it  is  obtained  from  a  permanent  fistula — then 
more  watery — or  from  a  newly-opened  duct.  The  solids  vary  in  a  tempo- 
rary^  fistula  from  80  to  100  parts  per  thousand,  and  in  a  permanent  one 
from  16  to  50  per  thousand. 

CHEMICAL  COMPOSITION  OF  THE  PANCREATIC  SECRETION. 

From  a  permanent  fistula.     (Bernstein.) 

Water         .         .         . 975 

Solids — Ferments : 

Proteids,  including  Serum — Albumin, Casein,  )    -,  -, 

Leucin  and  Tyrosin,  Fats  and  Soaps       .      j 
Inorganic  residue,  especially  Sodium  Carbonate  .     8 

25 


1000 

Functions. — (1.)  It  converts  proteids  into  peptones,  the  intermediate 
product  being  not  akin  to  syntonin  or  acid-albumin,  as  in  gastric  diges- 
tion, but  to  alkali-albumin.  Kiiline  believes  that  the  intermediate  pro- 
ducts, both  in  the  peptic  and  pancreatic  digestion  of  proteids,  are  two, 
viz.,  antialbumose  and  hemialbumose,  and  that  the  peptones  formed  cor- 
respond to  these,  viz.,  antipeptone  and  hemipeptone.  The  hemipeptone 
is  capable  of  being  converted  by  the  action  of  the  pancreatic  ferment — 


DIGESTION. 


267 


trypsin — into  leucin  and  tyrosin,  but  is  not  so  changed  by  pepsin;  the 
antipeptone  cannot  be  further  split  up.  The  products  of  pancreatic 
digestion  are  sometimes  further  complicated  by  the  appearance  of  certain 
faecal  substances,  of  which  iiidol  and  naphthilamine  are  the  most  impor- 
tant. (Kiilme.) 

When  the  digestion  goes  on  for  a  long  time  the  indol  is  formed  in  con- 
siderable quantities,  and  emits  a  most  disagreeable  faecal  odor,  which  was 
attributed  to  putrefaction  till  Kiihne  showed  its  true  nature.  All  the  al- 
buminous or  proteid  substances  which  have  not  been  converted  into  pep- 
tone, and  absorbed  in  the  stomach,  and  the  partially  changed  substances, 
i.r..  the  parapeptones,  are  converted  into  peptone  by  the  pancreatic  juice, 
and  then  in  part  into  leucin  and  tyrosin. 

(2.)  Nitrogenous  bodies  other  than  proteids,  are  not  to  any  extent 
altered.  Mucin  can,  however,  be  dissolved,  but  not  gelatin  or  horny  tis- 
sues. 

(3.)  Starch  is  converted  into  glucose  in  an  exactly  similar  manner  to 
that  which  happens  with  the  saliva.  As  mentioned  before,  it  seems  not 
unlikely  that  glucose  is  not  formed  at  once  from  starch,  but  that  certain 
dextrines  are  intermediate  products.  If  the  sugar  which  is  at  first  formed, 
as  is  stated  by  some  chemists,  be  not  glucose  but  maltose,  at  any  rate  the 
pancreatic  juice  after  a  time  completes  the  whole  change  of  starch  into 
glucose.  There  is  a  distinct  amylolytic  ferment  (Amylopsin)  in  the  pan- 
creatic juice  which  cannot  be  distinguished  from  ptyalin. 

(4.)  Oils  and  fats  are  both  emulsified  and  split  up  into  their  fatty 
acids  and  glycerin  by  pancreatic  secretion.  Even  if  part  of  this  action  is 
due  to  the  alkalinity  of  the  medium,  it  is  probable  that  there  is  a  third 
distinct  ferment  (Steapsin)  which  facilitates  the  change. 

Several  cases  have  been  recorded  in  which  the  pancreatic  duct  being 
obstructed,  so  that  its  secretion  could  not  be  discharged,  fatty  or  oily 
matter  was  abundantly  discharged  from  the  intestines.  In  nearly  all 
these  cases,  indeed,  the  liver  was  coincidently  diseased,  and  the  change 
or  absence  of  the  bile  might  appear  to  contribute  to  the  result;  yet  the 
frequency  of  extensive  disease  of  the  liver,  unaccompanied  by  fatty  dis- 
charges from  the  intestines,  favors  the  view  that,  in  these  cases,  it  is  to 
the  absence  of  the  pancreatic  fluid  from  the  intestines  that  the  excretion 
or  non-absorption  of  fatty  matter  should  be  ascribed. 

(5.)  It  possesses  the  property  of  curdling  milk,  containing  a  special 
(rennet)  ferment  for  that  purpose.  The  ferment  is  distinct  from  trypsin, 
and  will  act  in  the  presence  of  an  acid  (W.  Roberts). 

Conditions  favorable  to  the  Action  of  the  Pancreatic  Juice.— 
These  are  similar  to  those  which  are  favorable  to  the  action  of  the  saliva, 
and  the  reverse  (p.  231). 


268  HAND-BOOK    OF    PHYSIOLOGY. 


THE  LIVEE. 

The  Liver,  the  largest  gland  in  the  body,  situated  in  the  abdomen, 
chiefly  on  the  right  side,  is  an  extremely  vascular  organ,  and  receives  its 
supply  of  blood  from  two  distinct  vessels,  the  portal  vein  and  hepatic  ar- 
tery, while  the  blood  is  returned  from  it  into  the  vena  cava  inferior  by 
the  hepatic  veins.  Its  secretion,  the  bile,  is  conveyed  from  it  by  the 
hepatic  duct,  either  directly  into  the  intestine,  or,  when  digestion  is  not 
going  on,  into  the  cystic  duct,  and  thence  into  the  gall-bladder,  where  it 


FIG.  196. — The  under  surface  of  the  liver.  G.  B.,  gall-bladder;  H.  D.,  common  bile-duct;  H.  A., 
hepatic  artery;  v.  p.,  portal  vein;  L,  Q.,  lobulus  quadratus;  L.  s.,  lobulus  spigelii;  L.  c.,  lobulus  cau- 
datus;  D.-V.,  ductus  venosus;  u.  v.,  umbilical  vein.  (Noble  Smith.) 

accumulates  until  required.  The  portal  vein,  hepatic  artery,  and  hepatic 
duct  branch  together  throughout  the  liver,  while  the  hepatic  veins  and 
their  tributaries  run  by  themselves. 

On  the  outside  the  liver  has  an  incomplete  covering  of  peritoneum, 
and  beneath  this  is  a  very  fine  coat  of  areolar  tissue,  continuous  over  the 
whole  surface  of  the  organ.  It  is  thickest  where  the  peritoneum  is  absent, 
and  is  continuous  on  the  general  surface  of  the  liver  with  the  fine  and, 
in  the  human  subject,  almost  imperceptible,  areolar  tissue  investing  the 
lobules.  At  the  transverse  fissure  it  is  merged  in  the  areolar  investment 
called  Glisson's  capsule,  which,  surrounding  the  portal  vein,  hepatic  ar- 
tery, and  hepatic  duct,  as  they  enter  at  this  part,  accompanies  them  in 
their  branchings  through  the  substance  of  the  liver. 

Structure. — The  liver  is  made  up  of  small  roundish  or  oval  portions 
called  lobules,  each  of  which  is  about  -fa  of  an  inch  in  diameter,  and  com- 
posed of  the  minute  branches  of  the  portal  vein,  hepatic  artery,  hepatic 
duct,  and  hepatic  vein;  while  the  interstices  of  these  vessels  are  filled 
by  the  liver  cells.  The  hepatic  cells  (Fig.  197),  which  form  the  glandular 
or  secreting  part  of  the  liver,  are  of  a  spheroidal  form,  somewhat  polyg- 


DIGESTION. 


269 


onul  from  mutual  pressure  about  -^  to  T151jnr  inch  in  diameter,  possess- 
ing one,  sometimes  two  nuclei.  The  cell-substance  contains  numerous 
fatty  molecules,  and  some  yellowish-brown  granules  of  bile-pigment.  The 
cells  sometimes  exhibit  slow  amoeboid  movements.  They  are  held  to- 
gether by  a  very  delicate  sustentacular  tissue,  continuous  with  the  inter- 
lobular  connective  tissue. 

To  understand  the  distribution  of  the  blood-vessels  in  the  liver,  it 
will  be  well  to  trace,  first,  the  two  blood-vessels  and  the  duct  which  enter 
the  organ  on  the  under  surface  at  the  transverse  fissure,  viz.,  the  portal 
vein,  hepatic  artery,  and  hepatic  duct.  As  before  remarked,  all  three 
run  in  company,  and  their  appearance  on  longitudinal  section  is  shown  in 


FIG.  197. 


FIG.  198. 


FIG.  197.— A.  Liver-cells.    B,  Ditto,  containing  various  sized  particles  of  fat. 

FIG.  198. — Longitudinal  section  of  a  portal  canal,  containing  a  portal  vein,  hepatic  artery  and 
hepatic  duct,  from  the  pig.  P,  branch  of  vena  portae,  situate  in  a  portal  canal  formed  amongst  the 
lobules  of  the  liver,  1 1,  and  giving  off  vaginal  branches;  there  are  also  seen  within  the  large  portal 
vein  numerous  orifices  of  the  smallest  interlobular  veins  arising  directly  from  it;  a,  hepatic  artery; 
d,  hepatic  duct,  x  5.  (Kiernan.) 

Fig.  198.  Running  together  through  the  substance  of  the  liver,  they  are 
contained  in  small  channels  called  portal  canals,  their  immediate  invest- 
ment being  a  sheath  of  areolar  tissue  (Glisson's  capsule). 

To  take  the  distribution  of  the  portal  vein  first: — In  its  course  through 
the  liver  this  vessel  gives  off  small  branches  which  divide  and  subdivide 
between  the  lobules  surrounding  them  and  limiting  them,  and  from  this 
circumstance  called  inter-lobular  veins.  From  these  small  vessels  a  dense 
capillary  network  is  prolonged  into  the  substance  of  the  lobule,  and  this 
network,  gradually  gathering  itself  up,  so  to  speak,  into  larger  vessels, 
converges  finally  to  a  single  small  vein,  occupying  the  centre  of  the  lobule, 
and  hence  called  ^ra-lobular.  This  arrangement  is  well  seen  in  Fig. 
199,  which  represents  a  transverse  section  of  a  lobule. 


270 


HAND-BOOK    OF    PHYSIOLOGY. 


The  small  m^m-lobular  veins  discharge  their  contents  into  veins  called 
(h  h  h,  Fig.   200) ;  while  these  again,  by  their  union,  form 


FIG.  199.— Cross-section  of  a  lobule  of  the  human  liver,  in  which  the  capillary  network  between 
the  portal  and  hepatic  veins  has  been  fully  injected.  1,  section  of  the  mfra-lobular  vein;  2,  its  smaller 
branches  collecting  blood  from  the  capillary  network;  3,  tnfer-k>bular  branches  of  the  vena  portre 
with  their  smaller  ramifications  passing  inward  toward  the  capillary  network  in  the  substance  of 
the  lobule,  x  60.  (Sappey.) 


FIG.  200.— Section  of  a  portion  of  liver  passing  longitudinally  through  a  considerable  hepatic  vein, 
from  the  pig.  H,  hepatic  venous  trunk,  against  which  the  sides  of  the  lobules  (I)  are  applied;  /i,  7i,  7i, 
sublobular  hepatic  veins,  on  which  the  bases  of  the  lobules  rest,  and  through  the  coats  of  which  they 
are  seen  as  polygonal  figures;  t,  mouth  of  the  intralobular  veins,  opening  into  the  sublobular  veins; 
i',  intralobular  veins  shown  passing  up  the  centre  of  some  divided  lobules;  I,  I,  cut  surface  of  the 
liver;  c,  c,  walls  of  the  hepatic  venous  canal,  formed  by  the  polygonal  bases  of  the  lobules.  X  5. 
(Kiernan.) 

the  main  branches  of  the  hepatic  veins,  which  leave  the  posterior  border 
of  the  liver  to  end  by  two  or  three  principal  trunks  in  the  interior  vena 


DIGESTION. 


271 


cava,  just  before  its  passage  through  the  diaphragm.  The  swi-lobular 
and  hepatic  veins,  unlike  the  portal  vein  and  its  companions,  have  little 
or  no  areolar  tissue  around  them,  and  their  coats  being  very  thin,  they 
form  little  more  than  mere  channels  in  the  liver  substance  which  closely 
surrounds  them. 

The  manner  in  which  the  lobules  are  connected  with  the  sub-lobular 
veins  by  means  of  the  small  intra-lobular  veins  is  well  seen  in  the  diagram 
(Fig.  200  and  in  Fig.  201),  which  represent 
the  parts  as  seen  in  a  longitudinal  section. 
The  appearance  has  been  likened  to  a  twig 
having  leaves  without  footstalks — the  lobules 
representing  the  leaves,  and  the  sub-lobular 
vein  the  small  branch  from  which  it  springs. 
On  a  transverse  section,  the  appearance  of  the 
intra-lobular  veins  is  that  of  1,  Fig.  199, 
while  both  a  transverse  and  longitudinal  sec- 
tion are  exhibited  in  Fig.  176. 

The  hepatic  artery,  the  function  of  which 
is  to  distribute  blood  for  nutrition  to  Glisson's 
capsule,  the  walls  of  the  ducts  and  blood- 
vessels, and  other  parts  of  the  liver,  is  distrib- 
uted in  a  very  similar  manner  to  the  portal 
vein,  its  blood  being  returned  by  small  branches  either  into  the  rami- 
fications of  the  portal  vein,  or  into  the  capillary  plexus  of  the  lobules 
which  connects  the  inter  and  infra  lobular  veins. 


FIG.  201. — Diagram  showing  the 
manner  in  which  the  lobules  of  the 
liver  rest  on  the  sublobular  veins. 
(After  Kiernan.) 


Fia.  202. — Capillary  network  of  the  lobules  of  the  rabbit's  liver.  The  figure  is  taken  from  a  very 
•successful  injection  of  the  hepatic  veins,  made  by  Harting:  it  shows  nearly  the  whole  of  two  lobules, 
and  parts  of  three  others;  p,  portal  branches  running  in  the  interlobular  spaces;  h,  hepatic  veins  pen- 
etrating and  radiating  from  the  centre  of  the  lobules.  X  45.  (Kolliker.) 

The  hepatic  duct  divides  and  subdivides  in  a  manner  very  like  that  of 
the  portal  vein  and  hepatic  artery,  the  larger  branches  being  lined  by 
cylindrical,  and  the  smaller  by  small  polygonal  epithelium. 


272 


HAND-BOOK    OF    PHYSIOLOGY. 


The  bile-capillaries  commence  between  the  hepatic  cells,  and  are 
bounded  by  a  delicate  membranous  wall  of  their  own.  They  appear  to 
be  always  bounded  by  hepatic  cells  on  all  sides,  and  are  thus  separated 

from  the  nearest  blood-capillary  by  at  least  the 
breadth  of  one  cell  (Figs.  203  and  204). 

The  Gall-Bladder.— The  Gall-bladder  (G, 
B,  Fig.  196)  is  a  pyriform  bag,  attached  to  the 
under  surface  of  the  liver,  and  supported  also 
by  the  peritoneum,  which  passes  below  it.  The 
larger  end  or  fundus,  projects  beyond  the 
front  margin  of  the  liver;  while  the  smaller  end 
contracts  into  the  cystic  duct. 

Structure. — The  walls  of  the  gall-bladder 
are  constructed  of  three  principal  coats.  (1) 
Externally  (excepting  that  part  which  is  in 
contact  with  the  liver),  is  the  serous  coat, 
which  has  the  same  structure  as  the  peritoneum 
with  which  it  is  continuous.  Within  this  is 
(2)  the  fibrous  or  areolar  coat,  constructed  of 
tough  fibrous  and  elastic  tissue,  with  which  is 
mingled  a  considerable  number  of  plain  muscu- 
lar fibres,  both  longitudinal  and  circular.  (3)  Internally  the  gall-bladder 
is  lined  by  mucous  membrane,  and  a  layer  of  columnar  epithelium.  The 
surface  of  the  mucous  membrane  presents  to  the  naked  eye  a  minutely 
honeycombed  appearance  from  a  number  of  tiny  polygonal  depressions 
with  intervening  ridges,  by  which  its  surface  is  mapped  out.  In  the  cystic 


FIG.  203.— Portion  of  a  lobule  of 
liver,  a,  bile  capillaries  between 
liver-cells,  the  network  in  which 
is  well  seen;  6,  blood  capillaries. 
X  350.  (Klein  and  Noble  Smith.) 


FIG.  204.— Hepatic  cells  and  bile  capillaries,  from  the  liver  of  a  child  three  months  old.  Both  fig- 
ures  represent  fragments  of  a  section  carried  through  the  periphery  of  a  lobule.  The  red  corpuscles 
of  the  blood  are  recognized  by  their  circular  contour;  vp,  corresponds  to  an  interlobular  vein  in  im- 
mediate proximity  with  which  are  the  epithelial  cells  of  the  biliary  ducts,  to  which,  at  the  lower  part 
of  the  figures,  the  much  larger  hepatic  cells  suddenly  succeed.  (E.  Bering.) 

duct  the  mucous  membrane  is  raised  up  in  the  form  of  crescentic  folds, 
which  together  appear  like  a  spiral  valve,  and  which  minister  to  the 
function  of  the  gall-bladder  in  retaining  the  bile  during  the  intervals  of 
digestion. 


DIGESTION. 


273 


The  gall-bladder  and  all  the  main  biliary  ducts  are  provided  with 
mucous  glands,  which  open  on  their  internal  surface. 

Functions  of  the  Liver. — The  functions  of  the  Liver  may  be 
classified  under  the  following  heads: — 1.  The  Secretion  of  Bile.  2.  The 
Elaboration  of  Blood;  under  this  head  may  be  included  the  Glycogenic 
Function. 

I.    THE  SECRETION  OF  BILE. 

Properties  of  the  Bile. — The  bile  is  a  somewhat  viscid  fluid,  of  a 
yellow  or  reddish-yellow  color,  a  strongly  bitter  taste,  and,  when  fresh, 
with  a  scarcely  perceptible  odor:  it  has  a  neutral  or  slightly  alkaline  reac- 
tion, and  its  specific  gravity  is  about  1020.  Its  color  and  degree  of  con- 
sistence vary  much,  apparently  independent  of  disease;  but?  as  a  rule,  it 
becomes  gradually  more  deeply  colored  and  thicker  as  it  advances  along 
its  ducts,  or  when  it  remains  long  in  the  gall-bladder,  wherein,  at  the 
same  time,  it  becomes  more  viscid  and  ropy,  of  a  darker  color,  and  more 
bitter  taste,  mainly  from  its  greater  degree  of  concentration,  on  account 
of  partial  absorption  of  its  water,  but  partly  also  from  being  mixed  with 
mucus. 


Chemical  Composition  of  Human  Bile.     (Frerichs.) 


Water 
Solids 


Bile  salts  or  Bilin    . 

Fat          .... 

Cholesterin 

Mucus  and  coloring  matters 

Salts 


859-2 
140-8 

1000-0 

91-5 
9-2 
2.6 

29.8 

7-7 

140-8 


Bile  salts,  or  Bilin,  can  be  obtained  as  colorless,  exceedingly  deliques- 
cent crystals,  soluble  in  water,  alcohol,  and  alkaline  solutions,  giving  to- 
the  watery  solution  the  taste  and  general  characters  of  bile.  They  consist 
of  sodium  salts  of  glycocholic  and  taurocholic  acids.  The  former  salt  is 
composed  of  cholic  acid  conjugated  with  glycin  (see  Appendix),  the  latter 
of  the  same  acid  conjugated  with  taurin.  The  proportion  of  these  two- 
salts  in  the  bile  of  different  animals  varies,  e.g.,  in  ox  bile  the  glycocho- 
late  is  in  great  excess,  whereas  the  bile  of  the  dog,  cat,  bear,  and  other 
carnivora  contains  taurocholate  alone;  in  human  bile  both  are  present  in 
about  the  same  amount  (glycocholate  in  excess?). 

Preparation  of  Bile  Salt. — Bile  salts  may  be  prepared  in  the  fol- 
VOL.  I.— 18. 


274  HAND-BOOK    OF    PHYSIOLOGY. 

lowing  manner:  mix  bile  which  has  been  evaporated  to  a  quarter  of  its 
bulk  with  -animal  charcoal,  and  evaporate  to  perfect  dryness  in  a  water 
bath.  Next  extract  the  mass  whilst  still  warm  with  absolute  alcohol. 
Separate  the  alcoholic  extract  by  filtration,  and  to  it  add  perfectly  anhy- 
drous ether  as  long  as  a  precipitate  is  thrown  down.  The  solution  and 
precipitate  should  be  set  aside  in  a  closely  stoppered  bottle  for  some  days, 
when  crystals  of  the  bile  salts  or  bilin  will  have  separated  out.  The  gly- 
cocholate  may  be  separated  from  the  taurocholate  by  dissolving  bilin  in 
water,  and  adding  to  it  a  solution  of  neutral  lead  acetate,  and  then  a  little 
.basic  lead  acetate,  when  lead  glycocholate  separates  out.  Filter  and  add 
'to  the  filtrate  lead  acetate  and  ammonia,  a  precipitate  of  lead  taurocho- 
late will  be  formed,  which  may  be  filtered  off.  In  both  cases,  the  lead 
may  be  got  rid  of  by  suspending  or  dissolving  in  hot  alcohol,  adding 
hydrogen  sulphate,  filtering  and  allowing  the  acids  to  separate  out  by  the 
addition  of  water. 

The  test  for  bile  salts  is  known  as  Pettenkofer's.  If  to  an  aqueous 
solution  of  the  salts  strong  sulphuric  acid  be  added,  the  bile  acids  are  first 
of  all  precipitated,  but  on  the  further  addition  of  the  acid  are  re-dissolved. 
If  to  the  solution  a  drop  of  solution  of  cane  sugar  be  added,  a  fine  purple 
color  is  developed. 

The  re-action  will  also  occur  on  the  addition  of  grape  or  fruit  sugar 
instead  of  cane  sugar,  slowly  with  the  first,  quickly  with  the  last;  and  a 
color  similar  to  the  above  is  produced  by  the  action  of  sulphuric  acid  and 
sugar  on  albumen,  the  crystalline  lens,  nerve  tissue,  oleic  acid,  pure  ether, 
cholesterin,  morphia,  codeia  and  amylic  alcohol. 

The  spectrum  of  Pettenkofer's  reaction,  when  the  fluid  is  moderately 
diluted,  shows  four  bands — the  most  marked  and  largest  at  E,  and  a  little 
to  the  left;  another  at  F;  a  third  between  D  and  E,  nearer  to  D;  and 
the  fourth  near  D. 

The  yellow  coloring  matter  of  the  bile  of  man  and  the  Carnivora  is 
termed  Bilinibin  or  Bilifulvin  (cJ6HJ8N2o3)  crystallizable  and  insoluble  in 
water,  soluble  in  chloroform  or  carbon  disulphate;  a  green  coloring  matter, 
Biliverdin  (c16H20N2o6),  which  always  exists  in  large  amount  in  the  bile  of 
Herbivora,  being  formed  from  bilirubin  on  exposure  to  the  air,  or  by  sub- 
jecting the  bile  to  any  other  oxidizing  agency,  as  by  adding  nitric  acid. 
When  the  bile  has  been  long  in  the  gall-bladder,  a  third  pigment,  Bilipra- 
sin,  may  be  also  found  in  small  amount. 

In  cases  of  biliary  obstruction,  the  coloring  matter  of  the  bile  is  re- 
absorbed,  and  circulates  with  the  blood,  giving  to  the  tissues  the  yellow 
tint  characteristic  of  jaundice. 

The  coloring  matters  of  human  bile  do  not  appear  to  give  characteristic 
absorption  spectra;  but  the  bile  of  the  guinea  pig,  rabbit,  mouse,  sheep, 
ox,  and  crow  do  so,  the  most  constant  of  which  appears  to  be  a  band  at 


DIGESTION. 


275 


F.  The  bile  of  the  sheep  and  ox  give  three  bands  in  a  thick  layer,  and 
four  or  five  bands  with  a  thinner  layer,  one  on  each  side  of  D,  one  near 
E,  and  a  faint  line  at  F.  (McMunn.)  . 

There  seems  to  be  a  close  relationship  between  the  color-matter  of  the 
"blood  and  of  the  bile,  and  it  may  be  added,  between  these  and  that  of  the 
urine  (urobilin),  and  of  the  fa?ces  (stercobilin)  also;  -it  is  probable  they 
are,  all  of  them,  varieties  of  the  same  pigment,  or  derived  from  the  same 
source.  Indeed  it  is  maintained  that  Urobilin  is  identical  with  Hydro- 
bilirubin,  a  substance  which  is  obtained  from  bilirubin  by  the  action  of 
sodium  amalgam,  or  by  the  action  of  sodium  amalgam  on  alkaline  haema- 
tin;  both  urobilin  and  hydrobilirubin  giving  a  characteristic  absorption 
band  between  b  and  F.  They  are  also  identical  with  stercobilin,  which 
is  formed  in  the  alimentary  canal  from  bile  pigments. 

A  common  test  (Gmelin's)  for  the  presence  of  bile-pigment  consists  of 
the  addition  of  a  small  quantity  of  nitric  acid,  yellow  with  nitrous  acid; 
if  bile  be  present,  a  play  of  colors  is  produced,  beginning  with  green  and 
passing  through  blue  and  violet  to  red,  and  lastly  to  yellow.  The  spec- 
trum of  Gmelin's  test  gives  a  black  band 
extending  from  near  b  to  beyond  F. 

Fatty  substances  are  found  in  variable 
proportions  in  the  bile.  Besides  the  ordinary 
saponifiable  fats,  there  is  a  small  quantity 
of  ChoUsforin,  a  so-called  non-saponifiable 
fat,  which,  with  the  other  free  fats,  is  prob- 
ably held  in  solution  by  the  bile  salts.  It 
is  a  body  belonging  to  the  class  of  mon- 
atomic  alcohols  (c26H44o),  and  crystallizes  in 
rhombic  plates  (Fig.  205).  It  is  insoluble  in 
water  and  cold  alcohol,  but  dissolves  easily 
in  boiling  alcohol  or  ether.  It  gives  a  red 
color  with  strong  sulphuric  acid,  and  with  nitric  acid  and  ammonia;  also 
a  play  of  colors  beginning  with  blood  red  and  ending  with  green  on 
the  addition  of  sulphuric  acid  and  chloroform.  Lecithin  (c44H90^P09), 
a  phosphorus-containing  body  and  Neurin  (c6H1BNOa),  are  also  found  in 
bile,  the  latter  probably  as  a  decomposition  product  of  the  former. 

The  Mucus  in  bile  is  derived  from  the  mucous  membrane  and  glands 
of  the  gall-bladder,  and  of  the  hepatic  ducts.  It  constitutes  the  residue 
after  bile  is  treated  with  alcohol.  The  epithelium  with  which  it  is  mixed 
may  be  detected  in  the  bile  with  the  microscope  in  the  form  of  cylindrical 
cells,  either  scattered  or  still  held  together  in  layers.  To  the  presence  of 
the  mucus  is  probably  to  be  ascribed  the  rapid  decomposition  undergone 
by  the  bilin;  for,  according  to  Berzelius,  if  the  mucus  be  separated,  bile 
will  remain  unchanged  for  many  days. 

The  Saline  or   inorganic  constituents  of  the  bile  are  similar  to  those 


FIG.  205.— Crystalline  scales  of 
cholestefin. 


276  HAND-BOOK    OF    PHYSIOLOGY. 

found  in  most  other  secreted  fluids.  It  is  possible  that  the  carbonate  and 
neutral  phosphate  of  sodium  and  potassium,  found  in  the  ashes  of  bile, 
are  formed  in  the  incineration,  and  do  not  exist  as  such  in  the  fluid. 
Oxide  of  iron  is  said  to  be  a  common  constituent  of  the  ashes  of  bile,  and 
copper  is  generally  found  in  healthy  bile,  and  constantly  in  biliary  calculi. 

Gas — A  certain  .small  amount  of  carbonic  acid,  oxygen,  and  nitrogen, 
may  be  extracted  from  bile. 

Mode  of  Secretion  and  Discharge. — The  process  of  secreting  bile 
is  continually  going  on,  but  appears  to  be  retarded  during  fasting,  and 
accelerated  on  taking  food.  This  has  been  shown  by  tying  the  common 
bile-duct  of  a  dog,  and  establishing  a  fistulous  opening  between  the  skin 
and  gall-bladder,  whereby  all  the  bile  secreted  was  discharged  at  the  sur- 
face. It  was  noticed  that  when  the  animal  was  fasting,  sometimes  not  a 
drop  of  bile  was  discharged  for  several  hours;  but  that,  in  about  ten  min- 
utes after  the  introduction  of  food  into  the  stomach,  the  bile  began  to 
flow  abundantly,  and  continued  to  do  so  during  the  whole  period  of  diges- 
tion. (Blondlot,  Bidder  and  Schmidt.) 

The  bile  is  formed  in  the  hepatic  cells;  then,  being  discharged  into 
the  minute  hepatic  ducts,  it  passes  into  the  larger  trunks,  and  from  the 
main  hepatic  duct  maybe  carried  at  once  into  the  duodenum.  But,  prob- 
ably, this  happens  only  while  digestion  is  going  on;  during  fasting,  it 
regurgitates  from  the  common  bile-duct  through  the  cystic  duct,  into  the 
gall-bladder,  where  it  accumulates  till,  in  the  next  period  of  digestion,  it 
is  discharged  into  the  intestine.  The  gall-bladder  thus  fulfils  what  ap- 
pears to  be  its  chief  or  only  office,  that  of  a  reservoir;  for  its  presence 
enables  bile  to  be  constantly  secreted,  yet  insures  its  employment  in  the 
service  of  digestion,  although  digestion  is  periodic,  and  the  secretion  of 
bile  constant. 

The  mechanism  by  which  the  bile  passes  into  the  gall-bladder  is  sim- 
ple. The  orifice  through  which  the  common  bile-duct  communicates 
with  the  duodenum  is  narrower  than  the  duct,  and  appears  to  be  closed, 
except  when  there  is  sufficient  pressure  behind  to  force  the  bile  through 
it.  The  pressure  exercised  upon  the  bile  secreted  during  the  intervals  of 
digestion  appears  insufficient  to  overcome  the  force  with  which  the  ori- 
fice of  the  duct  is  closed;  and  the  bile  in  the  common  duct,  finding  no 
exit  in  the  intestine,  traverses  the  cystic  duct,  and  so  passes  into  the  gall- 
bladder, being  probably  aided-  in  this  retrograde  course  by  the  peristaltic 
action  of  the  ducts.  The  bile  is  discharged  from  the  gall-bladder  and 
enters  the  duodenum  on  the  introduction  of  food  into  the  small  intestine: 
being  pressed  on  by  the  contraction  of  the  coats  of  the  gall-bladder,  and 
of  the  common  bile-duct  also;  for  both  these  organs  contain  unstriped 
muscular  fibre-cells.  Their  contraction  is  excited  by  the  stimulus  of  the 
food  in  the  duodenum  acting  so  as  to  produce  a  reflex  movement,  the  force 
of  which  is  sufficient  to  open  the  orifice  of  the  common  bile-duct. 


DIGESTION. 


277 


Bile,  as  such,  is  not  pre-formed  in  the  blood.  As  just  observed,  it  is 
formed  by  the  hepatic  cells,  although  some  of  the  material  may  be  brought 
to  them  almost  in  the  condition  for  immediate  secretion.  When  it  is, 
however,  prevented  by  an  obstruction  of  some  kind,  from  escaping  into 
the  intestine  (as  by  the  passage  of  a  gall-stone  along  the  hepatic  duct)  it 
is  absorbed  in  great  excess  into  the  blood,  and,  circulating  with  it,  gives 
rise  to  the  well-known  phenomena  of  jaundice.  This  is  explained  by  the 
fact  that  the  pressure  of  secretion  in  the  ducts  is  normally  very  low,  and 
if  it  exceeds  f  inch  of  mercury  (16  mm.)  the  secretion  ceases  to  be  poured 
out,  and  if  the  opposing  force  be  increased,  the  bile  finds  its  way  into 
the  blood, 

Quantity. — Various  estimates  have  been  made  of  the  quantity  of  bile 
discharged  into  the  intestines  in  twenty-four  hours:  the  quantity  doubtless   ' 
varying,  like  that  of  the  gastric  fluid,  in  proportion  to  the  amount  of 
food  taken.     A  fair  average  of  several  computations  would  give  20  to 
40  oz.  (600 — 900  cc.)  as  the  quantity  daily  secreted  by  man. 

Uses. — (1)  As  an  excrementitious  substance,  the  bile  may  serve 
especially  as  a  medium  for  the  separation  of  excess  of  carbon  and  hydrogen 
from  the  blood;  and  its  adaptation  to  this  purpose  is  well  illustrated  by 
the  peculiarities  attending  its  secretion  and  disposal  in  the  foetus.  During 
intra-uterine  life,  the  lungs  and  the  intestinal  canal  are  almost  inactive; 
there  is  no  respiration  of  open  air  or  digestion  of  food;  these  are  unneces- 
sary, on  account  of  the  supply  of  well  elaborated  nutriment  received  by 
the  vessels  of  the  foetus  at  the  placenta.  The  liver,  during  the  same  time, 
is  proportionately  larger  than  it  is  after  birth,  and  the  secretion  of  bile  is 
active,  although  there  is  no  food  in  the  intestinal  canal  upon  which  it 
can  exercise  any  digestive  property.  At  birth,  the  intestinal  canal  is  full 
of  thick  bile,  mixed  with  intestinal  secretion;  the  meconium,  or  faeces  of 
the  foetus,  containing  all  the  essential  principles  of  bile. 


Composition  of  Meconium  (Frerichs) : 

Biliary  resin 

Common  fat  and  cholesterin 
Epithelium,  mucus,  pigment,  and  salts 


15.6 
15.4 
69.0 

100.0 


In  the  foetus,  therefore,  the  main  purpose  of  the  secretion  of  bile  must  be 
the  purification  of  blood  by  direct  excretion,  i.e.,  by  separation  from  the 
blood,  and  ejection  from  the  body  without  further  change.  Probably  all 
the  bile  secreted  in  foetal  life  is  incorporated  in  the  meconium,  and  with 
it  discharged,  and  thus  the  liver  may  be  said  to  discharge  a  function  in 
some  sense  vicarious  of  that  of  the  lungs.  For,  in  the  foetus,  nearly  all 
the  blood  coming  from  the  placenta  passes  through  the  liver,  previous  to 
its  distribution  to  the  several  organs  of  the  body;  and  the  abstraction  of 


278  HAKD-BOOK    OF    PHYSIOLOGY. 

carbon,  hydrogen,  and  other  elements  of  bile  will  purify  it,  as  in  extra- 
uterine  life  it  is  purified  by  the  separation  of  carbonic  acid  and  water  at 
the  lungs. 

The  evident  disposal  of  the  foetal  bile  by  excretion,  makes  it  highly 
probable  that  the  bile  in  extra-uterine  life  is  also,  at  least  in  part,  destined 
to  be  discharged  as  excrementitious.  The  analysis  of  the  faeces  of  both 
children  and  adults  shows  that  (except  when  rapidly  discharged  in  pur- 
gation) they  contain  very  little  of  the  bile  secreted,  probably  not  more 
than  one-sixteenth  part  of  its  weight,  and  that  this  portion  includes 
chiefly  its  coloring,  and  some  of  its  fatty  matters,  and  to  only  a  very 
slight  degree,  its  salts,  almost  all  of  which  have  been  re-absorbed  from 
the  intestines  into  the  blood. 

The  elementary  composition  of  bile  salts  shows,  however,  such  a  pre- 
ponderance of  carbon  and  hydrogen,  that  probably,  after  absorption,  it 
combines  with  oxygen,  and  is  excreted  in  the  form  of  carbonic  acid  and 
water.  The  change  after  birth,  from  the  direct  to  the  indirect  mode  of 
excretion  of  the  bile,  may,  with  much  probability,  be  connected  with  a 
purpose  in  relation  to  the  development  of  heat.  The  temperature  of  the 
foetus  is  maintained  by  that  of  the  parent,  and  needs  no  source  of  heat 
within  itself;  but,  in  extra-uterine  life,  there  is  (as  one  may  say)  a  waste 
of  material  for  heat  when  any  excretion  is  discharged  unoxidized;  the 
carbon  and  hydrogen  of  the  bilin,  therefore,  instead  of  being  ejected  in 
the  faeces,  are  re-absorbed,  in  order  that  they  may  be  combined  with 
oxygen,  and  that  in  the  combination  heat  may  be  generated. 

A  substance,  which  has  been  discovered  in  the  faeces,  and  named  ster- 
corin  is  closely  allied  to  cholesterin;  and  it  has  been  suggested  that  while 
one  great  function  of  the  liver  is  to  excrete  cholesterin  from  the  blood,  as 
the  kidney  excretes  urea,  the  stercorin  of  faeces  is  the  modified  form  in 
which  cholesterin  finally  leaves  the  body.  Ten  grains  and  a  half  of  ster- 
corin are  excreted  daily  (A.  Flint). 

From  the  peculiar  manner  in  which  the  liver  is  supplied  with  much 
of  the  blood  that  flows  through  it,  it  is  probable  that  this  organ  is  excre- 
tory, not  only  for  such  hydro-carbonaceous  matters  as  may  need  expulsion 
from  any  portion  of  the  blood,  but  that  it  serves  for  the  direct  purification 
of  the  stream  which,  arriving  by  the  portal  vein,  has  just  gathered  up 
various  substances  in  its  course  through  the  digestive  organs — substances 
which  may  need  to  be  expelled,  almost  immediately  after  their  absorption.- 
For  it  is  easily  conceivable  that  many  things  may  be  taken  up  during 
digestion,  which  not  only  are  unfit  for  purposes  of  nutrition,  but  which 
would  be  positively  injurious  if  allowed  to  mingle  with  the  general  mass 
of  the  blood.  The  liver,  therefore,  may  be  supposed  placed  in  the  only 
road  by  which  such  matters  can  pass  unchanged  into  the  general  current, 
jealously  to  guard  against  their  further  progress,  and  turn  them  back 
again  into  an  excretory  channel.  The  frequency  with  which  metallic 


DIGESTION.  279 

poisons  are  either  excreted  by  the  liver,  or  intercepted  and  retained,  often 
for  a  considerable  time,  in  its  own  substance,  may  be  adduced  as  evidence 
for  the  probable  truth  of  this  supposition. 

(2).  As  cf  digestive  fluid. — Though  one  chief  purpose  of  the  secretion 
of  bile  may  thus  appear  to  be  the  purification  of  the  blood  by  ultimate 
excretion,  yet  tli3re  are  many  reasons  for  believing  that,  while  it  is  in  the 
intestines,  it  performs  an  important  part  in  the  process  of  digestion.  In 
nearly  all  animals,  for  example,  the  bile  is  discharged,  not  through  an 
excretory  duct  communicating  with  the  external  surface  or  with  a  simple 
reservoir,  as  most  excretions  are,  but  is  made  to  pass  into  the  intestinal 
canal,  so  as  to  be  mingled  with  the  chyme  directly  after  it  leaves  the 
stomach;  an  arrangement,  the  constancy  of  which  clearly  indicates  that 
the  bile  has  some  important  relations  to  the  food  with  which  it  is  thus 
mixed.  A  similar  indication  is  furnished  also  by  the  fact  that  the  secre- 
tion of  bile  is  most  active,  and  the  quantity  discharged  into  the  intestines 
much  greater,  during  digestion  than  at  any  other  time;  although,  with- 
out doubt,  this  activity  of  secretion  during  digestion  may,  however,  be 
in  part  ascribed  to  the  fact  that  a  greater  quantity  of  blood  is  sent  through 
the  portal  vein  to  the  liver  at  this  time,  and  that  this  blood  contains  some 
of  the  materials  of  the  food  absorbed  from  the  stomach  and  intestines, 
which  may  need  to  be  excreted,  either  temporarily  (to  be  afterward  reab- 
sorbed)  or  permanently. 

Respecting  the  functions  discharged  by  the  bile  in  digestion  there  is 
little  doubt  that  it,  (a.)  assists  in  emulsifying  the  fatty  portions  of  the 
food,  and  thus  rendering  them  capable  of  being  absorbed  by  the  lacteals. 
For  it  has  appeared  in  some  experiments  in  which  the  common  bile-duct 
was  tied,  that,  although  the  process  of  digestion  in  the  stomach  was  un- 
aifected,  chyle  was  no  longer  well  formed;  the  contents  of  the  lacteals 
consisting  of  clear,  colorless  fluid,  instead  of  being  opaque  and  white,  as 
they  ordinarily  are,  after  feeding. 

(b.)  It  is  probable,  also,  that  the  moistening  of  the  mucous  membrane 
of  the  intestines  by  bile  facilitates  absorption  of  fatty  matters  through  it. 

(c.)  The  bile,  like  the  gastric  fluid,  has  a  considerable  antiseptic 
power,  and  may  serve  to  prevent  the  decomposition  of  food  during  the 
time  of  its  sojourn  in  the  intestines.  Experiments  show  that  the  con- 
tents of  the  intestines  are  much  more  foetid  after  the  common  bile-duct 
has  been  tied  than  at  other  times;  moreover,  it  is  found  that  the  mixture 
of  bile  with  a  fermenting  fluid  stops  or  spoils  the  process  of  fermentation. 

(d.)  The  bile  has  also  been  considered  to  act  as  a  natural  purgative, 
by  promoting  an  increased  secretion  of  the  intestinal  glands,  and  by 
stimulating  the  intestines  to  the  propulsion  of  their  contents.  This  view 
receives  support  from  the  constipation  which  ordinarily  exists  in  jaundice, 
from  the  diarrhoea  which  accompanies  excessive  secretion  of  bile,  and  from 
the  purgative  properties  of  ox-gall. 


280  HAND-BOOK    OF    PHYSIOLOGY. 

(e.)  The  bile  appears  to  have  the  power  of  precipitating  tlie  gastric 
parapeptones  and  peptones,  together  with  the  pepsin  which  is  mixed  up 
with  them,  as  soon  as  the  contents  of  the  stomach  meet  it  in  the  duo- 
denum. The  purpose  of  this  operation  is  probably  both  to  delay  any 
change  in  the  parapeptones  until  the  pancreatic  juice  can  act  upon  them, 
and  also  to  prevent  the  pepsin  from  exercising  its  solvent  action  on  the 
ferments  of  the  pancreatic  juice. 

Nothing  is  known  with  certainty  respecting  the  changes  which  the  re- 
absorbed  portions  of  the  bile  undergo.  That  they  are  much  changed 
appears  from  the  impossibility  of  detecting  them  in  the  blood;  and  that 
part  of  this  change  is  effected  in  the  liver  is  probable  from  an  experiment 
of  Magendie,  who  found  that  when  he  injected  bile  into  the  portal  vein, 
a  dog  was  unharmed,  but  was  killed  when  he  injected  the  bile  into  one  of 
the  systemic  vessels. 

II.  THE  LIVER  AS  A  BLOOD-ELABORATING  GLAND. 

The  secretion  of  bile,  as  already  observed,  is  only  one  of  the  purposes 
fulfilled  by  the  liver.  Another  very  important  function  appears  to  be 
that  of  so  acting  upon  certain  constituents  of  the  blood  passing  through 
it,  as  to  render  some  of  them  capable  of  assimilation  with  the  blood  gen- 
erally, and  to  prepare  others  for  being  duly  eliminated  in  the  process  of 
respiration.  It  appears  that  the  peptones,  conveyed  from  the  alimentary 
canal  by  the  blood  of  the  portal  vein,  require  to  be  submitted  to  the  influ- 
ence of  tne  liver  before  they  can  be  assimilated  by  the  blood;  for  if  such 
albuminous  matter  is  injected  into  the  jugular  vein,  it  speedily  appears  in 
the  urine;  but  if  introduced  into  the  portal  vein,  and  thus  allowed  to 
traverse  the  liver,  it  is  no  longer  ejected  as  a  foreign  substance,  but  is 
incorporated  with  the  albuminous  part  of  the  blood.  Albuminous  mat- 
ters are  also  subject  to  decomposition  by  the  liver  in  another  way  to  be 
immediately  noticed  (p.  281).  The  formation  of  urea  by  the  liver  will  be 
again  referred  to  (p.  371). 

Glycogenic  Function. — One  of  the  chief  uses  of  the  liver  in  connec- 
tion with  elaboration  of  the  blood  is  comprised  in  what  is  known  as  its 
glycogenic  function.  The  important  fact  that  the  liver  normally  forms 
glucose  or  grape  sugar,  or  a  substance  readily  convertible  into  it,  was  dis- 
covered by  Claude  Bernard  in  the  course  of  some  experiments  which  he 
undertook  for  the  purpose  of  finding  out  in  what  part  of  the  circulatory 
system  the  saccharine  matter  disappeared,  which  was  absorbed  from  the 
alimentary  canal.  With  this  purpose  he  fed  a  dog  for  seven  days  with 
food  containing  a  large  quantity  of  sugar  and  starch;  and,  as  might  be 
expected,  found  sugar  in  both  the  portal  and  hepatic  veins.  He  then 
fed  a  dog  with  meat  only,  and,  to  his  surprise,  still  found  sugar  in  the 


DIGESTION.  281 

hepatic  veins.  Repeated  experiments  gave  invariably  the  same  result;  no 
sugar  being  found,  under  a  meat  diet,  in  the  portal  vein>  if  care  were 
taken,  by  applying  a  ligature  on  it  at  the  transverse  fissure,  to  prevent 
reflux  of  blood  from  the  hepatic  venous  system.  Bernard  found  sugar 
also  in  the  substance  of  the  liver.  It  thus  seemed  certain  that  the  liver 
formed  sugar,  even  when,  from  the  absence  of  saccharine  and  amyloid 
matters  in  the  food,  none  could  be  brought  directly  to  it  from  the  stomach 
or  intestines. 

Excepting  cases  in  which  large  quantities  of  starch  and  sugar  were 
taken  as  food,  no  sugar  was  found  in  the  blood  after  it  had  passed  through 
the  lungs;  the  sugar  formed  by  the  liver,  having  presumably  disappeared 
by  combustion,  in  the  course  of  the  pulmonary  circulation. 

Bernard  found,  subsequently  to  the  before-mentioned  experiments, 
that  a  liver,  removed  from  the  body,  and  from  which  all  sugar  had  been 
completely  washed  away  by  injecting  a  stream  of  water  through  its  blood- 
vessels, will  be  found,  after  the  lapse  of  a  few  hours,  to  contain  sugar  in 
abundance.  This  post-mortem  production  of  sugar  was  a  fact  which  could 
only  be  explained  in  the  supposition  that  the  liver  contained  a  substance, 
readily  convertible  into  sugar  in  the  course  merely  of  post-mortem  decom- 
position; and  this  theory  was  proved  correct  by  the  discovery  of  a  sub- 
stance in  the  liver  allied  to  starch,  and  now  generally  termed  glycogen. 
We  may  believe,  therefore,  that  the  liver  does  not  form  sugar  directly 
from  the  materials  brought  to  it  by  the  blood,  but  that  glycogen  is  first 
formed  and  stored  in  its  substance;  and  that  the  sugar,  when  present,  is 
the  result  of  the  transformation  of  the  latter. 

Quantity  of  Glycogen  formed. — Although,  as  before  mentioned,  glyco- 
gen is  produced  by  the  liver  when  neither  starch  nor  sugar  is  present  in 
the  food,  its  amount  is  much  less  under  such  a  diet. 

Average  amount  of  Glycogen  in  the  Liver  of  Dogs  under  various  Diets. 

(Pavy.) 

Diet.  Amount  of  Glycogen  in  Liver. 

Animal  food ? -19  per  cent. 

Animal  food  with  sugar  (about  J  Ib.  of  sugar  daily)     14*5       " 
Vegetable  diet  (potatoes,  with  bread  or  barley-meal)     17  '23     " 

The  dependence  of  the  formation  of  glycogen  on  the  food  taken  is  also 
well  shown  by  the  following  results,  obtained  by  the  same  experimenter: 

Average  quantity  of  Glycogen  found  in  the  Liver  of  Rabbits  after  Fasting 
and  after  a  diet  of  Starch  and  Sugar  respectively. 

Average  amount  of  Glycogen  in  Liver. 

After  fasting  for  three  days         ....  Practically  absent. 
'*      diet  of  starch  and  grape-susrar   .         .         .  15*4  per  cent. 

.  16-9       " 


282  HAND-BOOK    OF    PHYSIOLOGY. 

Regarding  these  facts  there  is  no  dispute.  All  are  agreed  that  glyco- 
gen  is  formed,  and  laid  up  in  store,  temporarily,  by  the  liver-cells;  and 
that  it  is  not  formed  exclusively  from  saccharine  and  amylaceous  foods, 
but  from  albuminous  substances  also;  the  albumen,  in  the  latter  case, 
being  probably  split  up  into  glycogeii,  which  is  temporarily  stored  in  the 
liver,  and  urea,  which  is  excreted  by  the  kidneys. 

Destination  of  Glycogen. — There  are  two  chief  theories  on  the  sub- 
ject of  the  destination  of  glycogen.  (1.)  That  the  conversion  of  glycogen 
into  sugar  takes  place  rapidly  during  life  by  the  agency  of  a  ferment  also 
formed  in  the  liver:  and  the  sugar  is  conveyed  away  by  the  blood  of  the 
hepatic  veins,  and  soon  undergoes  combustion.  (2.)  That  the  conver- 
sion into  sugar  only  occurs  after  death,  and  that  during  life  no  sugar 
exists  in  healthy  livers;  glycogen  not  undergoing  this  transformation. 
The  chief  arguments  advanced  in  support  of  this  view  are,  (a)  that 
scarcely  a  trace  of  sugar  is  found  in  blood  drawn  during  life  from  the 
right  ventricle,  or  in  blood  collected  from  the  right  side  of  the  heart  im- 
mediately after  an  animal  has  been  killed;  while  if  the  examination  be 
delayed  for  a  very  short  time  after  death,  sugar  in  abundance  may  be 
found  in  such  blood;  (b),  that  the  liver,  like  the  venous  blood  in  the 
heart,  is,  at  the  moment  of  death,  completely  free  from  sugar,  although 
afterward  its  tissue  speedily  becomes  saccharine,  unless  the  formation  of 
sugar  be  prevented  by  freezing,  boiling,  or  other  means  calculated  to  in- 
terfere with  the  action  of  a  ferment  on  the  amyloid  substance  of  the 
organ.  Instead  of  adopting  Bernard's  view,  that  normally,  during  life, 
glycogen  passes  as  sugar  into  the  hepatic  venous  blood,  and  thereby  is 
conveyed  to  the  lungs  to  be  further  disposed  of,  Pavy  inclines  to  the 
belief  that  it  may  represent  an  intermediate  stage  in  the  formation  of  fat 
from  materials  absorbed  from  the  alimentary  canal. 

Liver-sugar  and  Glycogen. — To  demonstrate  the  presence  of  sugar 
in  the  liver,  a  portion  of  this  organ,  after  being  cut  into  small  pieces,  is 
bruised  in  a  mortar  to  a  pulp  with  a  small  quantity  of  water,  and  the 
pulp  is  boiled  with  sodium-sulphate  in  order  to  precipitate  albuminous 
and  coloring  matters.  The  decoction  is  then  filtered  and  may  be  tested 
for  glucose  (p.  230). 

Glycogen  (c6H10o&)  is  an  amorphous,  starch-like  substance,  odorless  and 
tasteless,  soluble  in  water,  insoluble  in  alcohol.  It  is  converted  into  glu- 
cose by  boiling  with  dilute  acids,  or  by  contact  with  any  animal  ferment. 
It  may  be  obtained  by  taking  a  portion  of  liver  from  a  recently  killed 
rabbit,  and,  after  cutting  it  into  small  pieces,  placing  it  for  a  short  time 
in  boiling  water.  It  is  then  bruised  in  a  mortar,  until  it  forms  a  pulpy 
mass,  and  subsequently  boiled  in  distilled  water  for  about  a  quarter  of  an 
hour.  The  glycogen  is  precipitated  from  the  filtered  decoction  by  the 
addition  of  alcohol.  Glycogen  has  been  found  in  many  other  structures 
than  the  liver.  (See  Appendix.) 


DIGESTION.  283 

Glycosuria. — The  facility  with  which  the  glycogen  of  the  liver  is 
transformed  into  sugar  would  lead  to  the  expectation  that  this  chemical 
change,  under  many  circumstances,  would  occur  to  such  an  extent  that 
sugar  would'  be  present  not  only  in  the  hepatic  veins,,  but  in  the  blood 
generally.  Such  is  frequently  the  case;  the  sugar  when  in  excess  in  the 
blood  being  secreted  by  the  kidneys,  and  thus  appearing  in  variable  quan- 
tities in  the  urine  (Glycosuria). 

Influence  of  the  Nervous  System  in  producing  Glycosuria. — 
Glycosuria  may  be  experimentally  produced  by  puncture  of  the  medulla 
oblongata  in  the  region  of  the  vaso-motor  centre.  The  better  fed  the 
animal  the  larger  is  the  amount  of  sugar  found  in  the  urine;  whereas  in 
the  case  of  a  starving  animal  no  sugar  appears.  It  is,  therefore,  highly 
probable  that  the  sugar  comes  from  the  hepatic  glycogeti,  since  in  the  one 
case  glycogen  is  in  excess,  and  in  the  other  it  is  almost  absent.  The 
nature  of  the  influence  is  uncertain.  It  may  be  exercised  in  dilating  the 
hepatic  vessels,  or  possibly  on  the  liver  cells  themselves.  The  whole 
course  of  the  nervous  stimulus  cannot  be  traced  to  the  liver,  but  at  first 
it  passes  from  the  medulla  down  the  spinal  cord  as  far  as — in  rabbits — 
the  fourth  dorsal  vertebra,  and  thence  to  the  first  thoracic  ganglion. 

Many  other  circumstances  will  cause  glycosuria.  It  has  been  observed 
after  the  administration  of  various  drugs,  after  the  injection  of  urari, 
poisoning  with  carbonic  oxide  gas,  the  inhalation  of  ether,  chloroform. 
etc.,  the  injection  of  oxygenated  blood  into  the  portal  venous  system.  It 
has  been  observed  in  man  after  injuries  to  the  head,  and  in  the  course  of 
various  diseases. 

The  well-known  disease,  didbetus  mellitus,  in  which  a  large  quantity 
of  sugar  is  persistently  secreted  daily  with  the  urine,  has,  doubtless,  some 
close  relation  to  the  normal  glycogenic  function  of  the  liver;  but  the 
nature  of  the  relationship  is  at  present  quite  unknown. 

The  Intestinal  Secretion,  or  Succus  Entericus.— On  account  of 
the  difficulty  in  isolating  the  secretion  of  the  glands  in  the  wall  of  the 
intestine  (Brunner's  and  Lieberkiihn's)  from  other  secretions  poured  into 
the  canal  (gastric  juice,  bile,  and  pancreatic  secretion),  but  little  is  known 
regarding  the  composition  of  the  former  fluid  (intestinal  juice,  succus  en- 
tericus). 

It  is  said  to  be  a  yellowish  alkaline  fluid  with  a  specific  gravity  of 
1011,  and  to  contain  about  2 -5  per  cent,  of  solid  matters  (Thiry). 

Functions. — The  secretion  of  Brunner's  glands  is  said  to  be  able  to 
convert  proteids  into  peptones,  and  that  of  Lieberkuhn's  is  believed  to 
convert  starch  into  sugar.  To  these  functions  of  the  succus  entericus  the 
powers  of  converting  cane  into  grape  sugar,  and  of  turning  cane  sugar 
into  lactic,  and  afterward  into  butyric  acid,  are  added  by  some 
physiologists.  It  also  probably  contains  a  milk-curdling  ferment  (W. 
Roberts). 


284  HAND-BOOK    OF   PHYSIOLOGY. 

The  reaction  which  represents  the  conversion  of  cane  sugar  into  grape 
sugar  may  be  represented  thus: — 

3C10HMOn    +    2H50    =    O.^.O,,    +    O.^O,, 

Saccharose  Water  Dextrose  Lsevulose 

The  conversion  is  probably  effected  by  means  of  a  hydrolytic  ferment. 
(Inversive  ferment,  Bernard.) 

The  length  and  complexity  of  the  digestive  tract  seem  to  be  closely 
connected  with  the  character  of  the  food  on  which  an  animal  lives.  Thus, 
in  all  carnivorous  animals,  such  as  the  cat  and  dog,  and  pre-eminently  in 
carnivorous  birds,  as  hawks  and  herons,  it  is  exceedingly  short.  The 
seals,  which,  though  carnivorous,  possess  a  very  long  intestine,  appear  to 
furnish  an  exception;  but  this  is  doubtless  to  be  explained  as  an  adaptation 
to  their  aquatic  habits:  their  constant  exposure  to  cold  requiring  that 
they  should  absorb  as  much  as  possible  from  their  intestines. 

Herbivorous  animals,  on  the  other  hand,  and  the  ruminants  especially, 
have  very  long  intestines  (in  the  sheep  30  times  the  length  of  the  body) 
which  is  no  doubt  to  be  connected  with  their  lowly  nutritious  diet.  In 
others,  such  as  the  rabbit,  though  the  intestines  are  not  excessively  long, 
this  is  compensated  by  the  great  length  and  capacity  of  the  caecum.  In 
man,  the  length  of  the  intestines  is  intermediate  between  the  extremes 
of  the  carnivora  and  herbivora,  and  his  diet  also  is  intermediate. 


Summary  of  the  Digestive  Changes  in  the  Small  Intestine. 

In  order  to  understand  the  changes  in  the  food  which  occur  during 
its  passage  through  the  small  intestine,  it  will  be  well  to  refer  briefly  to 
the  state  in  which  it  leaves  the  stomach  through  the  pylorus.  It  has 
been  said  before,  that  the  chief  office  of  the  stomach  is  not  only  to  mix 
into  a  uniform  mass  all  the  varieties  of  food  that  reach  it  through  the 
oesophagus,  but  especially  to  dissolve  the  nitrogenous  portion  by  means 
of  the  gastric  juice.  The  fatty  matters,  during  their  sojourn  in  the 
stomach,  become  more  thoroughly  mingled  with  the  other  constituents 
of  the  food  taken,  but  are  not  yet  in  a  state  fit  for  absorption.  The  con- 
version of  starch  into  sugar,  which  began  in  the  mouth,  has  been  inter- 
fered with,  if  not  altogether  stopped.  The  soluble  matters — both  those 
which  were  so  from  the  first,  as  sugar  and  saline  matter,  and  the  gastric 
peptones — have  begun  to  disappear  by  absorption  into  the  blood-vessels, 
and  the  same  thing  has  befallen  such  fluids  as  may  have  been  swallowed, 
— wine,  water,  etc. 

The  thin  pultaceous  chyme,  therefore,  which  during  the  whole  period 
of  gastric  digestion,  is  being  constantly  squeezed  or  strained  through  the 
pyloric  orifice  into  the  duodenum,  consists  of  albuminous  matter,  broken 
down,  dissolving  and  half  dissolved;  fatty  matter  broken  down  and 
melted,  but  not  dissolved  at  all;  starch  very  slowly  in  process  of  conversion 
into  sugar,  and  afi  it  becomes  sugar,  also  dissolving  in  the  fluids  with  which 


DIGESTION.  285 

it  is  mixed;  while,,  with  these  are  mingled  gastric  fluid,  and  fluid  that  has 
been  swallowed,  together  with  such  portions  of  the  food  as  are  not  digest- 
ible, and  will  be  finally  expelled  as  part  of  the  fseces. 

On  the  entrance  of  the  chyme  into  the  duodenum,  it  is  subjected  to 
the  influence  of  the  bile  and  pancreatic  juice,  which  are  then  poured  out, 
and  also  to  that  of  the  succus  entericus.  All  these  secretions  have  a  more 
or  less  alkaline  reaction,  and  by  their  admixture  with  the  gastric  chyme 
its  acidity  becomes  less  and  less  until  at  length,  at  about  the  middle  of 
the  small  intestine,  the  reaction  becomes  alkaline  and  continues  so  as  far 
as  the  ileo-csecal  valve. 

The  special  digestive  functions  of  the  small  intestine  may  be  taken  in 
the  following  order: — 

(1.)  One  important  duty  of  the  small  intestine  is  the  alteration  of  the 
fat  in  such  a  manner  as  to  make  it  fit  for  absorption;  and  there  is  no 
doubt  that  this  change  is  chiefly  effected  in  the  upper  part  of  the  small 
intestine.  What  is  the  exact  share  of  the  process,  however,  allotted  re- 
spectively to  the  bile,  to  the  pancreatic  secretion,  and  to  the  intestinal 
juice,  is  still  uncertain, — probably  the  pancreatic  juice  is  the  most  impor- 
tant. The  fat  is  changed  in  two  ways.  (a).  To  a  slight  extent  it  is 
chemically  decomposed  by  the  alkaline  secretions  with  which  it  is  mingled, 
and  a  soap  is  the  result,  (b).  It  is  emulsionized,  i.e.,  its  particles  are 
minutely  subdivided  and  diffused,  so  that  the  mixture  assumes  the  condi- 
tion of  a  milky  fluid,  or  emulsion.  As  will  be  seen  in  the  next  Chapter, 
most  of  the  fat  is  absorbed  by  the  lacteals  o2  the  intestine,  but  a  small 
part,  which  is  saponified,  is  also  absorbed  by  the  blood-vessels. 

(2.)  The  albuminous  substances  which  have  been  partly  dissolved  in 
the  stomach,  and  have  not  been  absorbed,  are  subjected  to  the  action  of 
the  pancreatic  and  intestinal  secretions.  The  pepsin  is  rendered  inert 
by  being  precipitated  together  with  the  gastric  peptones  and  parapeptones, 
as  soon  as  the  chyme  meets  with  bile.  By  these  means  the  pancreatic  fer- 
ment trypsin  is  enabled  to  proceed  with  the  further  conversion  of  the 
parapeptones  into  peptones,  and  of  part  of  the  peptones  (hemipeptone, 
Ktilme)  into  leucin  and  tyrosin.  Albuminous  substances,  which  are 
chemically  altered  in  the  process  of  digestion  (peptones),  and  gelatinous 
matters  similarly  changed,  are  absorbed  by  both  the  blood-vessels  and 
lymphatics  of  the  intestinal  mucous  membrane.  Albuminous  matters, 
in  a  state  of  solution,  which  have  not  undergone  the  peptonic  change,  are 
probably,  from  the  difficulty  with  which  they  diffuse,  absorbed,  if  at  all, 
almost  solely  by  the  lymphatics. 

(3.)  The  starchy,  or  amyloid  portions  of  the  food,  the  conversion  of 
which  into  dextrin  and  sugar  was  more  or  less  interrupted  during  its  stay 
in  the  stomach,  is  now  acted  on  briskly  by  the  pancreatic  juice  and  the 
succus  entericus;  and  the  sugar,  as  it  is  formed,  is  dissolved  in  the  intes- 
tinal fluids,  and  is  absorbed  chiefly  by  the  blood-vessels. 


286  HAND-BOOK    OF    PHYSIOLOGY. 

(4.)  Saline  and  saccharine  matters,  as  common  salt,  or  cane  sugar, 
if  not  in  a  state  of  solution  beforehand  in  the  saliva  or  other  fluids  which 
may  have  been  swallowed  with  them,  are  at  once  dissolved  in  the  stomach, 
and  if  not  here  absorbed,  are  soon  taken  up  in  the  small  intestine;  the 
blood-vessels,  as  in  the  last  case,  being  chiefly  concerned  in  the  absorp- 
tion. Cane  sugar  is  in  part  or  wholly  converted  into  grape-sugar  before 
its  absorption.  This  is  accomplished  partially  in  the  stomach,  but  also 
by  a  ferment  in  the  succus  entericus. 

(5.)  The  liquids,  including  in  this  term  the  ordinary  drinks,  as  water, 
wine,  ale,  tea,  etc.,  which  may  have  escaped  absorption  in  the  stomach, 
are  absorbed  probably  very  soon  after  their  entrance  into  the  intestine; 
the  fluidity  of  the  contents  of  the  latter  being  preserved  more  by  the  con- 
stant secretion  of  fluid  by  the  intestinal  glands,  pancreas,  and  liver,  than 
by  any  given  portion  of  fluid,  whether  swallowed  or  secreted,  remaining 
long  unabsorbed.  From  this  fact,  therefore,  it  may  be  gathered  that 
there  is  a  kind  of  circulation  constantly  proceeding  from  the  intestines 
into  the  blood,  and  from  the  blood  into  the  intestines  again;  for  as  all  the 
fluid — a  very  large  amount — secreted  by  the  intestinal  glands,  must  come 
from  the  blood,  the  latter  would  be  too  much  drained,  were  it  not  that 
the  same  fluid  after  secretion  is  again  re-absorbed  into  the  current  of  blood 
— going  into  the  blood  charged  with  nutrient  products  of  digestion — com- 
ing out  again  by  secretion  through  the  glands  in  a  comparatively  un- 
charged condition. 

At  the  lower  end  of  the  small  intestine,  the  chyme,  still  thin  and  pul- 
taceous,  is  of  a  light  yellow  color,  and  has  a  distinctly  faecal  odor.  This 
odor  depends  upon  the  formation  of  indol.  In  this  state  it  passes  through 
the  ileo-caecal  opening  into  the  large  intestine. 

SUMMARY  OF  THE  DIGESTIVE  CHANGES  IN  THE  LARGE  INTESTINE. 

The  changes  which  take  place  in  the  chyme  in  the  large  intestine  are 
probably  only  the  continuation  of  the  same  changes  that  occur  in  the 
course  ocf  the  food's  passage  through  the  upper  part  of  the  intestinal  canal. 
From  the  absence  of  villi,  however,  we  may  conclude  that  absorption, 
especially  of  fatty  matter,  is  in  great  part  completed  in  the  small  intes- 
tine; while,  from  the  still  half-liquid,  pultaceous  consistence  of  the  chyme 
when  it  first  enters  the  cagcum,  there  can  be  no  doubt  that  the  absorption 
of  liquid  is  not  by  any  means  concluded.  The  peculiar  odor,  moreover, 
which  is  acquired  after  a  short  time  by  the  contents  of  the  large  bowel, 
would  seem  to  indicate  a  further  chemical  change  in  the  alimentary  mat- 
ters or  in  the  digestive  fluids,  or  both.  The  acid  reaction,  which  had  dis- 
appeared in  the  small  bowel,  again  becomes  very  manifest  in  the  caecum 
— probably  from  acid  fermentation-processes  in  some  of  the  materials  of 
the  food. 


DIGESTION. 


287 


There  seems  no  reason  to  conclude  that  any  special  "secondary  diges- 
tive" process  occurs  in  the  csecurn  or  in  any  other  part  of  the  large  intestine. 
Probably  any  constituent  of  the  food  which  has  escaped  digestion  and 
absorption  in  the  small  bowel  may  be  digested  in  the  large  intestine;  and 
the  power  of  this  part  of  the  intestinal  canal  to  digest  fatty,  albuminous, 
or  other  matters,  may  be  gathered  from  the  good  effects  of  nutrient  ene- 
mata,  so  frequently  given  when  from  any  cause  there  is  difficulty  in  intro- 
ducing food  into  the  stomach.  In  ordinary  healthy  digestion,  however, 
the  changes  which  ensue  in  the  chyme  after  its  passage  into  the  large  in- 
testine, are  mainly  the  absorption  of  the  more  liquid  parts,  and  the  com- 
pletion of  the  changes  which  were  proceeding  in  the  small  intestine, — the 
process  being  assisted  by  the  secretion  of  the  numerous  tubular  glands 
therein  present. 

Faeces. — By  these  means  the  contents  of  the  large  intestine,  as  they 
proceed  toward  the  rectum,  become  more  and  more  solid,  and  losing  their 
more  liquid  and  nutrient  parts,  gradually  acquire  the  odor  and  consist- 
ence characteristic  of  faces.  After  a  sojourn  of  uncertain  duration  in 
the  sigmoid  flexure  of  the  colon,  or  in  the  rectum,  they  are  finally  ex- 
pelled by  the  act  of  defecation. 

The  average  quantity  of  solid  faseal  matter  evacuated  by  the  human 
adult  in  twenty-four  hours  is  about  six  or  eight  ounces. 


COMPOSITION  OF 

Water 733-00 

Solids 267-00 

Special  excrementitious  constituents: — Excretin, 
excretoleic  acid  (Marcet),  and  stercorin  (Aus- 
tin Flint). 

Salts: — Chiefly  phosphate  of  magnesium  and  phos- 
phate of  calcium,  with  small  quantities  of  iron, 
soda,  lime,  and  silica. 

Insoluble  residue  of  the  food  (chiefly  starch  grains, 

woody  tissue,  particles  of  cartilage  and  fibrous  \  267*00 
tissue,  undigested  muscular  fibres  or  fat,  and 
the  like,  with  insoluble  substances  accidentally 
introduced  with  the  food). 

Mucus,  epithelium,  altered  coloring  matter  of  bile, 
fatty  acids,  etc. 

Varying  quantities  of  other  constituents  o.f  bile, 
and  derivatives  from  them. 

Length  of  Intestinal  Digestive  Period.— The  time  occupied  by 
the  journey  of  a  given  portion  of  food  from  the  stomach  to  the  anus, 
varies  considerably  even  in  health,  and  on  this  account,  probably,  it  is 
that  such  different  opinions  have  been  expressed  in  regard  to  the  subject. 
About  twelve  hours  are  occupied  by  the  journey  of  an  ordinary  meal 


288  HAND-BOOK    OF    PHYSIOLOGY. 

through  the  small  intestine,  and  twenty-four  to  thirty-six  hours  by  the 
passage  through  the  large  bowel.  (Brinton.) 

Defalcation. — Immediately  before  the  act  of  voluntary  expulsion  of 
faeces  (defcecation)  there  is  usually,  first  an  inspiration,  as  in  the  case  of 
coughing,  sneezing,  ancl  vomiting;  the  glottis  is  then  closed,  and  the 
diaphragm  fixed.  The  abdominal  muscles  are  contracted  as  in  expira- 
tion; but  as  the  glottis  is  closed,  the  whole  of  their  pressure  is  exercised 
on  the  abdominal  contents.  The  sphincter  of  the  rectum  being  relaxed, 
the  evacuation  of  its  contents  takes  place  accordingly;  the  effect  being, 
of  course,  increased  by  the  peristaltic  action  of  the  intestine.  As  in  the 
other  actions  just  referred  to,  there  is  as  much  tendency  to  the  escape  of 
the  contents  of  the  lungs  or  stomach  as  of  the  rectum;  but  the  pressure 
is  relieved  only  at  the  orifice,  the  sphincter  of  which  instinctively  or  in- 
voluntarily yields  (see  Fig.  144). 

Nervous  Mechanism  of  Defaecation. — The  anal  sphincter  muscle 
is  normally  in  a  state  of  tonic  contraction.  The  nervous  centre  which 
governs  this  contraction  is  probably  situated  in  the  lumbar  region  of  the 
spinal  cord,  inasmuch  as  in  cases  of  division  of  the  cord  above  this  region 
the  sphincter  regains,  after  a  time,  to  some  extent  the  tonicity  which  is 
lost  immediately  after  the  operation.  By  an  effort  of  the  will,  acting 
through  the  centre,  the  contraction  may  be  relaxed  or  increased.  In  ordi- 
nary cases  the  apparatus  is  set  in  action  by  the  gradual  accumulation  of 
faeces  in  the  sigmoid  flexure  and  rectum  pressing  against  the  sphincter 
and  causing  its  relaxation;  this  sensory  impulse  acting  through  the  brain 
and  reflexly  through  the  spinal  centre.  Peristaltic  action,  especially  of  the 
sigmoid  flexure  in  pressing  onward  the  faeces  against  the  sphincter,  is  a 
very  important  part  of  the  act. 

The  Gases  contained  in  the  Stomach  and  Intestines. — Under 
ordinary  circumstances,  the  alimentary  canal  contains  a  considerable 
quantity  of  gaseous  matter.  Any  one  who  has  had  occasion,  in  a  post- 
mortem examination,  either  to  lay  open  the  intestines,  or  to  let  out  the 
gas  which  they  contain,  must  have  been  struck  by  the  small  space  after- 
ward occupied  by  the  bowels,  and  by  the  large  degree,  therefore,  in  which 
the  gas,  which  naturally  distends  them,  contributes  to  fill  the  cavity  of 
the  abdomen.  Indeed,  the  presence  of  air  in  the  intestines  is  so  constant, 
and,  within  certain  limits,  the  amount  in  health  so  uniform,  that  there 
can  be  no  doubt  that  its  existence  here  is  not  a  mere  accident,  but  in- 
tended to  serve  a  definite  and  important  purpose,  although,  probably,  a 
mechanical  one. 

Sources. — The  sources  of  the  gas  contained  in  the  stomach  and 
bowels  may  be  thus  enumerated: — 

1.  Air  introduced  in  the  act  of  swallowing  either  food  or  saliva;  2. 
Gases  developed  by  the  decomposition  of   alimentary  matter  or  of  the 


DIGESTION. 


289 


secretions  and  excretions  mingled  with  it  in  the  stomach  and  intestines; 
3.  It  is  probable  that  a  certain  mutual  interchange  occurs  between  the 
gases  contained  in  the  alimentary  canal,  and  those  present  in  the  blood 
of  these  gastric  and  intestinal  blood-vessels;  but  the  conditions  of  the 
exchange  are^not  known,  and  it  is  very  doubtful  whether  anything  like  a 
true  and  definite  secretion  of  gas  from  the  blflod  into  the  intestines  or 
stomach  ever  takes  place.  There  can  be  no  doubt,  however,  that  the  in- 
testines may  be  the  proper  excretory  organs  for  many  odorous  and  other 
substances,  either  absorbed  from  the  air  taken  into  the  lungs  in  inspira- 
tion, or  absorbed  in  the  upper  part  of  the  alimentary  canal,  again  to  be 
excreted  at  a  portion  of  the  same  tract  lower  down — in  either  case  as- 
suming rapidly  a  gaseous  form  after  their  excretion,  and  in  this  way, 
perhaps,  obtaining  a  more  ready  egress  from  the  body.  It  is  probable- 
that,  under  ordinary  circumstances,  the  gases  of  the  stomach  and  intes- 
tines are  derived  chiefly  from  the  second  of  the  sources  which  have  been 
enumerated  (Brinton). 


COMPOSITION  OF  GASES  CONTAINED  IN  THE  ALIMENTARY  CANAL. 
(TABULATED  FROM  VARIOUS  AUTHORITIES  BY  BRINTON.) 


Whence  obtained. 

Composition  by  Volume. 

Oxygen. 

Nitrog. 

Carbon. 
Acid. 

Hydrog. 

Carburet. 
Hydrogen. 

Sulphuret. 
Hydrogen. 

Stomach     
Small  Intestines  . 
Caecum  

11 

71 

32 
66 
35 
46 
22 

14 
30 
12 

57 
43 
41 

4 
38 

8 
6 

19 

13 

8 
11 
19 

1     . 

y  trace 

i 

Colon     
Rectum      
Expelled  per  anum  .     . 

Movements  of  the  Intestines. — It  remains  only  to  consider  the 
manner  in  which  the  food  and  the  several  secretions  mingled  with  it  are 
moved  through  the  ftitestinal  canal,  so  as  to  be  slowly  subjected  to  the 
influence  of  fresh  portions  of  intestinal  secretion,  and  as  slowly  exposed 
to  the  absorbent  power  of  all  the  villi  and  blood-vessels  of  the  mucous 
membrane.  The  movement  of  the  intestines  is  peristaltic  or  vermicular, 
and  is  effected  by  the  alternate  contractions  and  dilatations  of  successive 
portions  of  the  intestinal  coats.  The  contractions,  which  may  commence 
at  any  point  of  the  intestine,  extend  in  a  wave-like  manner  along  the  tube. 
In  any  given  portion,  the  longitudinal  muscular  fibres  contract  first,  or 
more  than  the  circular;  they  draw  a  portion  of  the  intestine  upward,  or, 
as  it  were,  backward,  over  the  substance  to  be  propelled,  and  then  the 
circular  fibres  of  the  same  portion  contracting  in  succession  from  above 
downward,  or,  as  it  were,  from  behind  forward,  press  on  the  substance 
into  the  portion  next  below,  in  which  at  once  the  same  succession  of  action 
next  ensues.  These  movements  take  place  slowly,  and,  in  health,  are  com- 
VOL.  I.— 19. 


290  HAND-BOOK    OF    PHYSIOLOGY. 

monly  unperceived  by  the  mind;  but  they  are  perceptible  when  they  are 
accelerated  under  the  influence  of  any  irritant. 

The  movements  of  the  intestines  are  sometimes  retrograde;  and  there 
is  no  hindrance  to  the  backward  movement  of  the  contents  of  the  small 
intestine.  But  almost  ^complete  security  is  aiforded  against  the  passage 
of  the  contents  of  the  large  into  the  small  intestine  by  the  ileo-caecal 
valve.  Besides, — the  orifice  of  communication  between  the  ileum  and 
caecum  (at  the  borders  of  which  orifice  are  the  folds  of  mucous  membrane 
which  form  the  valve)  is  encircled  with  muscular  fibres,  the  contraction 
of  which  prevents  the  undue  dilatation  of  the  orifice. 

Proceeding  from  above  downward,  the  muscular  fibres  of  the  large 
intestine  become,  on  the  whole,  stronger  in  direct  proportion  to  the  greater 
strength  required  for  the  onward  moving  of  the  faeces,  which  are  gradually 
becoming  firmer.  The  greatest  strength  is  in  the  rectum,  at  the  termi- 
nation of  which  the  circular  unstriped  muscular  fibres  form  a  strong  band 
called  the  internal  sphincter;  while  an  external  sphincter  muscle  with 
striped  fibres  is  placed  rather  lower  down,  and  more  externally,  and  as 
we  have  seen  above,  holds  the  orifice  close  by  a  constant  slight  tonic  con- 
traction. 

Experimental  irritation  of  the  brain  or  cord  produces  no  evident  or  con- 
stant effect  on  the  movements  of  the  intestines  during  li^e;  yet  in  conse- 
quence of  certain  conditions  of  the  mind  the  movements  are  accelerated  or 
retarded;  and  in  paraplegia  the  intestines  appear  after  a  time  much  weak- 
ened in  their  power,  and  costiveness,  with  a  tympanitic  condition,  ensues. 
Immediately  after  death,  irritation  of  both  the  sympathetic  and  pneumo- 
gastric  nerves,  if  not  too  strong,  induces  genuine  peristaltic  movements  of 
the  intestines.  Violent  irritation  stops  the  movements.  These  stimuli  act, 
no  doubt,  not  directly  on  the  muscular  tissue  of  the  intestine,  but  on  the 
ganglionic  plexus  before  referred  to. 

Influence  of  the  Nervous  System  on  Intestinal  Digestion.— 
As  in  the  case  of  the  oesophagus  and  stomach,  the  peVistaltic  movements  of 
the  intestines  are  directly  due  to  reflex  action  through  the  ganglia  and  nerve 
fibres  distributed  so  abundantly  in  their  walls  (p.  255);  the  presence  of 
chyme  acting  as  the  stimulus,  and  few  or  no  movements  occurring  when 
the  intestines  are  empty.  The  intestines  are,  moreover,  connected  with 
the  higher  nerve-centres  by  the  splanchnic  nerves,  as  well  as  other 
branches  of  the  sympathetic  which  come  to  them  from  the  coeliac  and 
other  abdominal  plexuses. 

The  splanchnic  nerves  are  in  relation  to  the  intestinal  movements, 
inhibitory — these  movements  being  retarded  or  stopped  when  the  splanch- 
nics  are  irritated.  As  the  vaso-motor  nerves  of  the  intestines,  the  splanch- 
nics  are  also  much  concerned  in  intestinal  digestion. 


CHAPTER    IX. 

ABSORPTION. 

THE  process  of  Absorption  has,  for  one  of  its  objects,  the  introduction 
into  the  blood  of  fresh  materials  from  the  food  and  air,  and  of  whatever 
comes  into  contact  with  the  external  or  internal  surfaces  of  the  body; 
and,  for  another,  the  gradual  removal  of  parts  of  the  body  itself,  when 
they  need  to  be  renewed.  In  both  these  offices,  i.e.,  in  both  absorption 
from  without  and  absorption  from  within,  the  process  manifests  some 
variety,  and  a  very  wide  range  of  action;  and  in  both  two  sets  of  vessels 
are,  or  may  be,  concerned,  namely,  the  Blood-vessels,  and  the  Lymph- 
vessels  or  Lymphatics  to  which  the  term  Absorbents  has  been  also  applied. 

THE  LYMPHATIC  VESSELS  AND  GLANDS. 

Distribution. — The  principal  vessels  of  the  lymphatic  system  are,  in 
structure  and  general  appearance,  like  very  small  and  thin-walled  veins, 
and  like  them  are  provided  with  valves.  By  one  extremity  they  com- 
mence by  fine  microscopic  branches,  the  lymphatic  capillaries  or  lymph- 
t"/ 'Maries,  in  the  organs  and  tissues  of  the  body,  and  by  their  other  ex- 
tremities they  end  directly  or  indirectly  in  two  trunks  which  open  into  the 
large  veins  near  the  heart  (Fig.  206).  Their  contents,  the  lymph  and 
Stifle,  unlike  the  blood,  pass  only  in  one  direction,  namely,  from  the  fine 
1  tranches  to  the  trunk  and  so  to  the  large  veins,  on  entering  which  they 
are  mingled  with  the  stream  of  blood,  and  form  part  of  its  constituents. 
Remembering  the  course  of  the  fluid  in  the  lymphatic  vessels,  viz.,  its 
passage  in  the  direction  only  toward  the  large  veins  in  the  neighborhood 
of  the  heart,  it  will  readily  be  seen  from  Fig.  206  that  the  greater  part  of 
the  contents  of  the  lymphatic  system  of  vessels  passes  through  a  com- 
paratively large  trunk  called  the  thoracic  duct,  which  finally  empties  its 
contents  into  the  blood-stream,  at  the  junction  of  the  internal  jugular 
and  subclavian  veins  of  the  left  side.  There  is  a  smaller  duct  on  the 
right  side.  The  lymphatic  vessels  of  the  intestinal  canal  are  called  lacteals, 
because,  during  digestion,  the  fluid  contained  in  them  resembles  milk  in 
appearance;  and  the  lymph  in  the  lacteals  during  the  period  of  digestion 
is  called  chyle.  There  is  no  essential  distinction,  however,  between  lac- 


292  HAND-BOOK    OF    PHYSIOLOGY. 

teals  and  lymphatics.     In  some  parts  of  their  course  all  lymphatic  vessels 
pass  through  certain  bodies  called  lymphatic  glands. 

Lymphatic  vessels  are  distributed  in  nearly  all  parts  of  the  body. 
Their  existence,  however,  has  not  yet  been  determined  in  the  placenta,  the 
umbilical  cord,  the  membranes  of  the  ovum,  or  in  any  of  the  non-vascular 
parts,  as  the  nails,  cuticle,  hair  and  the  like. 

Lymphatics    of    head   and     I^IBWftRnMHiHKHIiBS!     Lymphatics   of    head    and 
neck,  right.  BHBBgftflifggii  KYffSB  neck'  left 

Right  internal  jugular  vein.  Hflin!          Thoracic  duct. 

Right  subclavian  vein SWiMS 

E^feifc/  vB     XfflSf&BK&n  subclavian  vein. 

Lymphatics  of  right  arm.  . 


Thoracic  duct. 


Receptaculum  chyli. 

Lacteals. 


Lymphatics  of    lower    ex-  m**T$&  S aSS  I    Lymphatics  of    lower    ex- 

tremities. S^5JtS9^9B;i^3H  tremities. 

Q^BMliin&w^lBKKflOTlamiSBB 

FIG.  206.— Diagram  of  the  principal  groups  of  lymphatic  vessels  (from  Quain). 

Origin  of  Lymph  Capillaries. — The  lymphatic  capillaries  com- 
mence most  commonly  either  in  closely-meshed  networks,  or  in  irregular 
lacunar  spaces  between  the  various  structures  of  which  the  different 
organs  are  composed.  Such  irregular  spaces,  forming  what  is  now 
termed  the  lymph-canalicular  system,  have  been  shown  to  exist  in  many 
tissues.  In  serous  membranes,  such  as  the  omentum  and  mesentery,  they 
occur  as  a  connected  system  of  very  irregular  branched  spaces  partly  occu- 
pied by  connective-tissue  corpuscles,  and  both  in  these  and  in  many  other 
tissues  are  found  to  communicate  freely  with  regular  lymphatic  vessels. 
In  many  cases,  though  they  are  formed  mostly  by  the  chinks  and  crannies 
between  the  blood-vessels,  secreting  ducts,  and  other  parts  which  may 


ABSORPTION. 

happen  to  form  the  framework  of  the  organ  in  which  they  exist,  they 
are  lined  by  a  distinct  layer  of  endothelium. 

The  lacteals  offer  an  illustration  of  another  mode  of  origin,  namely, 
in  blind  dilated  extremities  (Figs.  192  and  193);  but  there  is  no  essen- 
tial difference  in  structure  between  these  and  the  lymphatic  capillaries  of 
other  parts. 

Structure  of  Lymph  Capillaries. — The  structure  of  lymphatic 
capillaries  is  very  similar  to  that  of  blood-capillaries:  their  walls  consist 
of  a  single  layer  of  endothelial  cells  of  an  elongated  form  and  sinuous 
outline,  which  cohere  along  their  edges  to  form  a  delicate  membrane. 


Fio.  207.—  Lymphatics  of  central  tendon  of  rabbit's  diaphragm,  stained  with  silver  nitrate.  The 
ground  substance  has  been  shaded  diagrammatically  to  bring  out  the  lymphatics  clearly.  I.  Lym- 
phatics lined  by  long  narrow  endothelial  cells,  and  showing  v.  valves  at  frequent  intervals  (Schofleld). 


They  differ  from  blood  capillaries  mainly  in  their  larger  and  very  varia- 
ble calibre,  and  in  their  numerous  communications  with  the  spaces  of 
the  lymph-canalicular  system. 

Communications  of  the  Lymphatics.— The  fluid  part  of  the  blood 
constantly  exudes  or  is  strained  through  the  walls  of  the  blood-capillaries, 
so  as  to  moisten  all  the  surrounding  tissues,  and  occupies  the  interspaces 
which  exist  among  their  different  elements.  These  same  interspaces  have 
been  shown,  as  just  stated,  to  form  the  beginnings  of  the  lymph-capilla- 
ries; and  the  latter,  therefore,  are  the  means  of  collecting  the  exuded 
blood-plasma,  and  returning  that  part  which  is  not  directly  absorbed  by 
the  tissues  into  the  blood-stream.  For  many  years,  the  notion  of  the 
existence  of  any  such  channels  between  the  blood-vessels  and  lymph-ves- 
sels as  would  admit  blood-corpuscles,  has  been  given  up;  observations 
having  proved  that,  for  the  passage  of  such  corpuscles,  it  is  not  necessary 


294 


HAND-BOOK    OF    PHYSIOLOGY. 


to  assume  the  presence  of  any  special  channels  at  all,  inasmuch  as  blood- 
corpuscles  can  pass  bodily,  without  much  difficulty,  through  the  walls  of 
the  blood-capillaries  and  small  veins  (p.  159),  and  could  pass  with  still 
less  trouble,  probably,  through  the  comparatively  ill-defined  walls  of  the 
capillaries  which  contain  lymph. 


FIG.  208. — Lymphatic  vessels  of  the  head  and  neck  and  the  upper  part  of  the  trunk  (Mascagni). 
1-6.— The  chest  and  pericardium  have  been  opened  on  the  left  side,  and  the  left  mamma  detached  and 
thrown  outward  over  the  left  arm,  so  as  to  expose  a  great  part  of  its  deep  surface.  The  principal 
lymphatic  vessels  and  glands  are  shown  on  the  side  of  the  head  and  face,  and  in  the  neck,  axilla,  and 
mediastinum.  Between  the  left  internal  jugular  vein  and  the  common  carotid  artery,  the  upper  as- 
cending part  of  the  thoracic  duct  marked  1,  and  above  this,  and  descending  to  2,  the  arch  and  last 
part  of  the  duct.  The  termination  of  the  upper  lymphatics  of  the  diaphragm  in  the  mediastinal 
glands,  as  well  as  the  cardiac  and  the  deep  mammary  lymphatics,  is  also  shown: 

It  is  worthy  of  note  that,  in  many  animals,  both  arteries  and  veins, 
especially  the  latter,  are  often  found  to  be  more  or  less  completely  eii- 
sheathed  in  large  lymphatic  channels.  In  turtles,  crocodiles,  and  many 
other  animals,  the  abdominal  aorta  is  enclosed  in  a  large  lymphatic  vessel. 

Stomata. — In  certain  parts  of  the  body  openings  exist  by  which 
lymphatic  capillaries  directly  communicate  with  parts  hitherto  supposed 
to  be  closed  cavities.  If  the  peritoneal  cavity  be  injected  with  milk,  an 
injection  is  obtained  of  the  plexus  of  lymphatic  vessels  of  the  central 
tendon  of  the  diaphragm  (Fig.  207);  and  on  removing  a  small  portion  of 
the  central  tendon,  with  its  peritoneal  surface  uninjured,  and  examining 


ABSORPTION. 


295 


the  process  of  absorption  under  the  microscope,  the  milk-globules  run 
toward  small  natural  openings  or  stomata  between  the  epithelial  cells,  and 
disappear  by  parsing  vortex-like  through  them.  The  stomata,  which 
have  a  roundish  outline,  are  only  wide  enough  to  admit  two  or  three  milk- 
globules  abreast,  and  never  exceed  the  size  of  an  epithelial  cell. 


FIG.  209. 


FIG.  210. 


FIG.  209.— Superficial  lymphatics  of  the  forearm  and  palm  of  the  hand,  1-5.  5.  Two  small  glands 
at  the  bend  of  the  arm.  6."Radial  lymphatic  vessels.  7.  Ulnar  lymphatic  vessels.  8,  8.  Palmar  arch 
of  lymphatics.  9,  9.  Outer  and  inner  sets  of  vessels,  b.  Cephalic  vein.  d.  Radial  vein.  e.  Median 
vein.  /.  Ulnar  vein.  The  lymphatics  are  represented  as  lying  on  the  deep  fascia.  (Mascagni.) 

FIG.  210.— Superficial  lymphatics  of  right  groin  and  upper  part  of  thigh,  1-6.  1,  upper  inguinal 
glands.  2,  2',  Lower  inguinal  or  femoral  glands.  3,  3'.  Plexus  of  lymphatics  in  the  course  of  the 
long  saphenous  vein.  (Mascagni.) 

Pseudostomata. —  When  absorption  into  the  lymphatic  system  takes 
place  in  membranes  covered  by  epithelium  or  endothelium  through  the 
interstitial  or  intercellular  cement-substance,  it  is  said  to  take  place 
through  pseudostomata. 


296  HAND-BOOK    OF    PHYSIOLOGY. 

Demonstration  of  Lymphatics  of  Diaphragm. — The  stomata  on  the 
peritoneal  surface  of  the  diaphragm  are  the  openings  of  short  vertical 
canals  which  lead  up  into  the  lymphatics,  and  are  lined  by  cells  like  those 
of  germinating  endothelium  (p.  23).  By  introducing  a  solution  of  Berlin 
blue  into  the  peritoneal  cavity  of  an  animal  shortly  after  death,  and  sus- 
pending it,  head  downward,  an  injection  of  the  lymphatic  vessels  of  the 
diaphragm,  through  the  stomata  on  its  peritoneal  surface,  may  readily  be 
obtained,  if  artificial  respiration  be  carried  on  for  about  half  an  hour.  In 
this  way  it  has  been  found  that  in  the  rabbit  the  lymphatics  are  arranged 
between  the  tendon  bundles  of  the  centrum  tendineum;  and  they  are 
hence  termed  interfascicular.  The  centrum  tendineum  is  coated  by 
endothelium  on  its  pleural  and  peritoneal  surfaces,  and  its  substance  con- 
sists of  tendon  bundles  arranged  in  concentric  rings  toward  the  pleural 
side  and  in  radiating  bundles  toward  the  peritoneal  side. 


FIG.  21 1  .—Peritoneal  surface  of  septum  cisternae  lymphaticee  magnee  of  frog.  The  stomata,  some 
of  which  are  open,  some  collapsed,  are  surrounded  by  germinating  endothelium.  x  160.  (Klein.) 

The  lymphatics  of  the  anterior  half  of  the  diaphragm  open  into  those 
of  the  anterior  mediastinum,  while  those  of  the  posterior  half  pass  into  a 
lymphatic  vessel  in  the  posterior  mediastinum,  which  soon  enters  the  tho- 
racic duct.  Both  these  sets  of  vessels,  and  the  glands  into  which  they 
pass,  are  readily  injected  by  the  method  above  described;  and  there  can 
be  little  doubt  that  during  life  the  flow  of  lymph  along  these  channels  is 
chiefly  caused  by  the  action  of  the  diaphragm  during  respiration.  As 
it  descends  in  inspiration,  the  spaces  between  the  radiating  tendon  bun- 
dles dilate,  and  lymph  is  sucked  from  the  peritoneal  cavity,  through  the 
widely  open  stomata,  into  the  interfascicular  lymphatics.  .During  expira- 
tion, the  spaces  between  the  concentric  tendon  bundles  dilate,  and  the 
lymph  is  squeezed  into  the  lymphatics  toward  the  pleural  surface.  (Klein. ) 
It  thus  appears  probable  that  during  health  there  is  a  continued  sucking 
in  of  lymph  from  the  .peritoneum  into  the  lymphatics  by  the  "pumping" 
action  of  the  diaphragm;  and  there  is  doubtless  an  equally  continuous 
exudation  of  fluid  from  the  general  serous  surface  of  the  peritoneum. 
When  this  balance  of  transudation  and  absorption  is  disturbed,  either  by 
increased  transudation  or  some  impediment  to  absorption,  an  accumula- 
tion of  fluid  necessarily  takes  place  (ascites). 

Stomata  have  been  found  in  the  pleura;  and  as  they  may  be  presumed 
to  exist  in  other  serous  membranes,  it  would  seem  as  if  the  serous  cavities, 


ABSORPTION.  297 

hitherto  supposed  closed,  form  but  a,  large  lymph-sinus,  or  widening  out, 
so  to  speak,  of  the  lymph-capillary  system  with  which  they  directly  com- 
municate. 

Structure  of  Lymphatic  Vessels.— The  larger  vessels  are  very  like 
veins,  having  an  external  coat  of  fibro-cellular  tissue,  with  elastic  fila- 
ments; within  this,  a  thin  layer  of  nbro-cellular  tissue,  with  plain  mus- 
cular fibres,  which  have,  principally,  a  circular  direction,  and  are  much 
more  abundant  in  the  small  than  in  the  larger  vessels;  and  again,  within 
this,  an  inner  elastic  layer  of  longitudinal  fibres,  and  a  lining  of  epithe- 
lium; and  numerous  valves.  The  valves,  constructed  like  those  of  veins, 
and  with  the  free  edges  turned  toward  the  heart,  are  usually  arranged  in 
pairs,  and,  in  the  small  vessels,  are  so  closely  placed,  that  when  the  vessels 
are  full,  the  valves  constricting  them  where  their  edges  are  attached,  give 
them  a  peculiar  beaded  or  knotted  appearance. 

Current  of  the  Lymph. — With  the  help  of  the  valvular  mechanism 
(1)  all  occasional  pressure  on  the  exterior  of  the  lymphatic  and  lacteal 
vessels  propels  the  lympK  toward  the  heart:  thus  muscular  and  other 
external  pressure  accelerates  the  flow  of  the  lymph  as  it  does  that  of  the 
blood  in  the  veins.  The  actions  of  (2)  the  muscular  fibres  of  the  small 
intestine,  and  probably  the  layer  of  organic  muscle  present  in  each  intes- 
tinal villus,  seem  to  assist  in  propelling  the  chyle:  for,  in  the  small  intes- 
tine of  a  mouse,  the  chyle  has  been  seen  moving  with  intermittent  pro- 
pulsions that  appeared  to  correspond  with  the  peristaltic  movements  of 
the  intestine.  But  for  the  general  propulsion  of  the  lymph  and  chyle,  it 
is  probable  that,  together  with  (3)  the  vis  a  tergo  resulting  from  absorp- 
tion (as  in  the  ascent  of  sap  in  a  tree),  and  from  external  pressure,  some 
of  the  force  may  be  derived  (4)  from  the  contractility  of  the  vessel's  own 
walls.  The  respiratory  movements,  also,  (5)  favor  the  current  of  lymph 
through  the  thoracic  duct  as  they  do  the  current  of  blood  in  the  thoracic 
veins  (p.  206). 

Lymphatic  Glands  are  small  round  or  oval  compact  bodies  varying 
in  size  from  a  hempseed  to  a  bean,  interposed  in  the  course  of  the  lym- 
phatic vessels,  and  through  which  the  chief  part  of  the  lymph  passes  in 
its  course  to  be  discharged  into  the  blood-vessels.  They  are  found  in 
<*reat  numbers  in  the  mesentery,  and  along  the  great  vessels  of  the  abdo- 
jnen,  thorax,  and  neck;  in  the  axilla  and  groin;  a  few  in  the  popliteal 
space,  but  not  further  down  the  leg,  and  in  the  arm  as  far  as  the  elbow. 
Some  lymphatics  do  not,  however,  pass  through  glands  before  entering 
the  thoracic  duct. 

Structure. — A  lymphatic  gland  is  covered  externally  by  a  capsule  of 
connective  tissue,  generally  containing  some  unstriped  muscle.  At  the 
inner  side  of  the  gland,  which  is  somewhat  concave  (hilus)  (Fig.  212,  a), 
the  capsule  sends  processes  inward  in  which  the  blood-vessels  are  con- 
tained, and  these  join  with  other  processes  called  trabeculce  (Fig.  215,  t.r.) 


298 


HAND-BOOK    OF    PHYSIOLOGY. 


prolonged  from  the  inner  surface  of  the  part  of  the  capsule  covering  the 
convex  or  outer  part  of  the  gland;  they  have  a  structure  similar  to  that 
of  the  capsule,  and  entering  the  gland  from  all  sides,  and  freely  commu- 
nicating, form  a  fibrous  supporting  stroma.  The  interior  of  the  gland 
is  seen  on  section,  even  when  examined  with  the  naked  eye,  to  be  made 
up  of  two  parts,  an  outer  or  cortical  (Fig.  212,  c,  c),  which  is  light- 
colored,  and  an  inner  of  redder  appearance,  the  medullary  portion  (Fig. 
212).  In  the  outer  or  cortical  part  of  the  gland  (Fig.  215,  c)  the  inter- 
vals between  the  trabeculse  are  comparatively  large  and  more  or  less  trian- 


FIG.  212. 


FIG.  213. 


FIG.  212.— Section  of  a  mesenteric  gland  f  rom  the  ox,  slightly  magnified,  a,  Hilus;  b  (in  the  cen- 
tral part  of  the  figure),  medullary  substance;  c,  cortical  substance  with  indistinct  alveoli;  d,  capsule 
(Kolliker.) 

FIG.  213.— From  a  vertical  section  through  the  capsule,  cortical  sinus  and  peripheral  portion  of 
follicle  of  a  human  compound  lymphatic  gland.  The  section  had  been  shaken,  so  as  to  get  rid  of  most 
of  the  lymph  corpuscles.  A.  Outer  stratum  of  capsule,  consisting  of  bundles  of  fibrous  tissue  cut  at 
various  angles.  B.  Inner  stratum,  showing  fibres  of  connective  tissue  with  nuclei  of  flattened  con- 
nective-tissue-corpuscles. Beneath  this  (between  B  and  C)  is  the  lymph-sinus  or  lymph-path,  contain- 
ing a  reticulum  coated  by  flat  nucleated  endothelial  cells.  C.  Fine  nucleated  endothelial  membrane, 
marking  boundary  of  the  lymph-follicle.  The  rest  of  the  section  from  C  to  E  is  the  adenoid  tissue  of 
the  lymph-follicle,  which  consists  of  a  fine  reticulum,  E,  with  numerous  lymph-corpuscles,  D.  They 
are  so  closely  packed  that  the  adenoid  reticulum  is  invisible  till  the  section  has  been  shaken  so  as  to 
dislodge  a  number  of  the  lymph-corpuscles,  x  350.  (Klein  and  Isoble  Smith.) 

gular,  the  intercommunicating  spaces  being  termed  alveoli;  whilst  in  the 
more  central  or  medullary  part  a  finer  mesh  work  is  formed  by  the  more 
free  anastomosis  of  the  trabecular  processes.  In  the  alveoli  of  the  cortex 
and  in  the  mesh  work  formed  by  the  trabeculae  in  the  medulla,  is  contained 
the  proper  gland  structure.  In  the  former  it  is  arranged  as  follows  (Fig. 
215):  occupying  the  central  and  chief  part  of  each  alveolus,  is  a  more  or 
less  wedge-shaped  mass  (l.h.)  of  adenoid  tissue,  densely  packed  with  lymph 
corpuscles;  but  at  the  periphery  surrounding  the  central  portion  and  im- 
mediately next  the  capsule  and  trabeculaa,  is  a  more  open  meshwork  of 
adenoid  tissue  constituting  the  lymph  sinus  or  channel  (Is.),  and  contain- 


AHSORPTIOX. 


209 


ing  fewer  lymph  corpuscles.  The  central  mass  is  enclosed  in  endothelium, 
the  cells  of  which  join  by  their  processes,  the  processes  of  the  adenoid 
framework  of  the  lymph  sinus.  The  trabeculse  are  also  covered  with 
endothelium'.  The  lining  of  the  central  mass  does  not  prevent  the  passage 


FIG.  214.— Section  of  medullary  substance  of  an  inguinal  gland  of  an  ox:  a,  a,  glandular  substance- 
or  pulp  forming  rounded  cords  joining  in  a  continuous  net  (dark  in  the  figure):  c,  c,  trabeculse;  the 
space,  b.  b.  between  these  and  the  glandular  substance  is  the  lymph-sinus,  washed  clear  of  corpuscles- 
and  traversed  by  filaments  of  retiform  connective-tissue,  x  90.  (Kolliker.) 


tr- 


Fift.  215.— Diagrammatic  section  of  Lymphatic  gland,  a.  I.,  Afferent;  e.  L,  efferent  lymphatics^ 
C,  cortical  substance:  I.  h.,  reticulating  cords  of  medullary  substance:  I.  ».,  lymph-sinus;  c.,  fibrous 
coat  sending  in  trabeculre;  t.  r.,  into  the  substance  of  the  gland.  (Sharpey.) 

of  fluids  and  even  of  corpuscles  into  the  lymph  sinus.  The  framework  of 
the  adenoid  tissue  of  the  lymph  sinus  is  nucleated,  that  of  the  central 
mass  is  non-nucleated.  At  the  inner  part  of  the  alveolus,  the  wedge- 


300 


HAND-BOOK    OF    PHYSIOLOGY. 


.shaped  central  mass  bifurcates  (Fig.  215)  or  divides  into  two  or  more 
.smaller  rounded  or  cord-like  masses,  and  here  joining  with  those  from  the 
other  alveoli,  form  a  much  closer  arrangement  of  the  gland  tissue  (Fig. 
214,  a)  than  in  the  cortex;  spaces  (Fig.  214,  b)  are  left  within  those 
anastomosing  cords,  in  which  are  found  portions  of  the  trabecular  mesh- 
work  and  the  continuation  of  the  lymph  sinus  (b,  c). 

The  essential  structure  of  lymphatic-gland  substance  resembles  that 
which  was  described  as  existing,  in  a  simple  form,  in  the  interior  of  the 
solitary  and  agminated  intestinal  follicles. 

The  lymph  enters  the  gland  by  several  afferent  vessels  (Fig.  215,  a.L) 
which  open  beneath  the  capsule  into  the  lymph -channel  or  lymph-path; 


FIG.  216. — A  small  portion  of  medullary  substance  from  a  mesenteric  gland  of  the  ox.  d,  d,  tra- 
beculae;  a,  part  of  a  cord  of  glandular  substances  from  which  all  but  a  few  of  the  lymph-corpuscles 
have  been  washed  out  to  show  its  supporting  meshwork  of  retiform  tissue  and  its  capillary  blood-ves- 
sels (which  have  been  injected,  and  are  dark  in  the  figure);  6,  6,  lymph-sinus,  of  which  the  retiform 
tissue  is  represented  only  at  c,  c.  X  300.  (.Kolliker.) 

.at  the  same  time  they  lay  aside  all  their  coats  except  the  endothelial 
lining,  which  h  continuous  with  the  lining  of  the  lymph-path.  The 
efferent  vessels  (Fig.  215,  e.l. )  begin  in  the  medullary  part  of  the  gland, 
and  are  continuous  with  the  lymph-path  here  as  the  aiferent  vessels  were 
with  the  cortical  portion;  the  endothelium  of  one  is  continuous  with  that 
of  the  other. 

The  efferent  vessels  leave  the  gland  at  the  hilus,  the  more  or  less  con- 
cave inner  side  of  the  gland,  and  generally  either  at  once  or  very  soon 
after  join  together  to  form  a  single  vessel. 

Blood-vessels  which  enter  and  leave  the  gland  at  the  hilus  are  freely 
distributed  to  the  trabecular  tissue  and  to  the  gland-pulp  (Fig.  216). 


ABSORPTION.  301 

The  tonsils,  in  part,  and  Beyer's  glands  of  -the  intestine,  are  really 
lymphatic  glands,  and  doubtless  discharge  similar  functions. 

THE  LYMPH  AND  CHYLE. 

The  lymph,  contained  in  the  lymphatic  vessels,  is,  under  ordinary  cir- 
cumstances, a  clear,  transparent,  and  yellowish  fluid.  It  is  devoid  of 
smell,  is  slightly  alkali  ae,  and  has  a  saline  taste.  As  seen  with  the 
microscope  in  the  small  transparent  vessels  of  the  tail  of  the  tadpole,  it 
usually  contains  no  corpuscles  or  particles  of  any  kind;  and  it  is  only  in 
the  larger  trunks  in  which  any  corpuscles  are  to  be  found.  These  corpus- 
cles are  similar  to  colorless  blood-corpuscles.  The  fluid  in  which  the  cor- 
puscles float  is  albuminous,  and  contains  no  fatty  particles  or  molecular  base; 
but  is  liable  to  variations  according  to  the  general  state  of  the  blood,  and 
to  that  of  the  organ  from  which  the  lymph  is  derived.  As  it  advances- 
toward  the  thoracic  duct,  and  after  passing  through  the  lymphatic  glands, 
it  becomes  spontaneously  coagulable  and  the  number  of  corpuscles  is  much, 
increased.  The  fluid  contained  in  the  lacteals  is  clear  and  transparent 
during  fasting,  and  differs  in  no  respect  from  ordinary  lymph;  but,  during 
digestion,  it  becomes  milky,  and  is  termed  chyle. 

Chyle  is  an  opaque,  whitish,  milky  fluid,  neutral  or  slightly  alkaline 
in  reaction.  Its  whiteness  and  opacity  are  due  to  the  presence  of  innu- 
merable particles  of  oily  or  fatty  matter,  of  exceedingly  minute  though 
nearly  uniform  size,  measuring  on  the  average  about  yg-J-g-g-  of  an  inch. 
These  constitute  what  is  termed  the  molecular  base  of  chyle.  Their 
number,  and  consequently  the  opacity  of  the  chyle,  are  dependent  upon 
the  quantity  of  fatty  matter  contained  in  the  food.  The  fatty  nature  of 
the  molecules  is  made  manifest  by  their  solubility  in  ether,  and,  when 
the  ether  evaporates,  by  their  being  deposited  in  various-sized  drops  of 
oil.  Each  molecule  probably  consists  of  oil  coated  over  with  albumen,  in 
the  manner  in  which  oil  always  becomes  covered  when  set  free  in  minute 
drops  in  an  albuminous  solution.  This  is  proved  when  water  or  dilute 
acetic  acid  is  added  to  chyle,  many  of  the  molecules  are  lost  sight  of,  and 
oil-drops  appear  in  their  place,  as  the  investments  of  the  molecules  have 
been  dissolved,  and  their  oily  contents  have  run  together. 

Except  these  molecules,  the  chyle  taken  from  the  villi  or  from  lacteals 
near  them,  contains  no  other  solid  or  organized  bodies.  The  fluid  in 
which  the  molecules  float  is  albuminous,  and  does  not  spontaneously 
coagulate.  But  as  the  chyle  passes  on  toward  the  thoracic  duct,  and 
especially,  while  it  traverses  one  or  more  of  the  mesenteric  glands,  it  is 
elaborated.  The  quantity  of  molecules  and  oily  particles  gradually  dimin- 
ishes; cells,  to  which  the  name  of  chyle-corpuscles  is  given,  are  devel- 
oped in  it;  and  it  acquires  the  property  of  coagulating  spontaneously. 
The  higher  in  the  thoracic  duct  the  chyle  advances,  the  more  is  it,  in  all 


302  HAND-BOOK    OF    PHYSIOLOGY. 

these  respects,  developed;  the  greater  is  the  number  of  chyle-corpuscles, 
and  the  larger  and  firmer  is  the  clot  which  forms  in  it  when  withdrawn 
and  left  at  rest.  Such  a  clot  is  like  one  of  blood  without  the  red  cor- 
puscles, having  the  chyle  corpuscles  entangled  in  it,  and  the  fatty  matter 
forming  a  white  creamy  film  on  the  surface  of  the  serum.  But  the  clot 
of  chyle  is  softer  and  moister  than  that  of  blood.  Like  blood,  also,  the 
chyle  often  remains  for  a  long  time  in  its  vessels  without  coagulating,  but 
coagulates  rapidly  on  being  removed  from  them.  The  existence  of  the 
materials  which,  by  their  union,  form  fibrin,  is,  therefore,  certain;  and 
their  increase  appears  to  be  commensurate  with  that  of  the  corpuscles. 

The  structure  of  the  chyle-corpuscles  was  described  when  speaking  of 
the  white  corpuscles  of  the  blood,  with  which  they  are  identical. 

Chemical  Composition  of  Lymph  and  Chyle. — From  what  has 
been  said,  it  will  appear  that  perfect  chyle  and  lymph  are,  in  essential 
characters,  nearly  similar,  and  scarcely  diifer,  except  in  the  preponder- 
ance of  fatty  and  proteid  matter  in  the  chyle. 


CHEMICAL  COMPOSITION  OF  LYMPH  AND  CHYLE.     (Owen  Eees.) 

i.  ii.  in. 

Lymph  Chyle       Mixed  Lymph  & 

(Donkey).      (Donkey).    Chyle  (Human). 

Water          ....     96*536         90-237    "        90-48 
Solids  3-454  9 '763  9-52 


Solids— 

Proteids,  including  Serum- 
Albumin,  Fibrin,  and 
Globulin 

Extractives,  including  in  (i 
and  i)  Sugar,  Urea,  Leu- 
cin  and  Cholesterin 

Fatty  matter 


1-320  3-886  7-08 


1.559  1-565  -108 

a  trace          3 -601  -92 


Salts        ....         -585  -711  -44 

From  the  above  analyses  of  lymph  and  chyle,  it  appears  that  they  con- 
tain essentially  the  same  constituents  that  are  found  in  the  blood.  Their 
composition,  indeed,  differs  from  that  of  the  blood  in  degree  rather  than 
in  kind.  They  do  not,  however,  unless  by  accident,  contain  colored  cor- 
puscles. 

Quantity. — The  quantity  which  would  pass  into  a  cat's  blood  in 
twenty-four  hours  has  been  estimated  to  be  equal  to  about  one-sixth  of 
the  weight  of  the  whole  body.  And,  since  the  estimated  weight  of  the 
blood  in  cats  is  to  the  weight  of  their  bodies  as  1  -7,  the  quantity  of  lymph 
daily  traversing  the  thoracic  duct  would  appear  to  be  about  equal  to  the 
quantity  of  blood  at  any  time  contained  in  the  animals.  By  another  series 


ABSORPTION.  303 

of  experiments,  the  quantity  of  lymph  traversing  the  thoracic  duct  of  a 
dog  in  twenty-four  hours  was  found  to  be  about  equal  to  two-thirds  of 
the  blood  in  the  body.  (Bidder  and  Schmidt.) 

Absorption  by  the  Lacteals. — During  the  passage  of  the  chyme 
along  the  whole  tract  of  the  intestinal  canal,  its  completely  digested  parts 
are  absorbed  by  the  blood-vessels  and  lacteals  distributed  in  the  mucous 
membrane.  The  blood-vessels  appear  to  absorb  chiefly  the  dissolved  por- 
tions of  the  food,  and  these,  including  especially  the  albuminous  and  sac- 
charine, they  imbibe  without  choice;  whatever  can  mix  with  the  blood 
passes  into  the  vessels,  as  will  be  presently  described.  But  the  lacteals 
appear  to  absorb  only  certain  constituents  of  the  food,  including  par- 
ticularly the  fatty  portions.  The  absorption  by  both  sets  of  vessels  is 
carried  on  most  actively  but  not  exclusively,  in  the  villi  of  the  small  in* 
tcstine;  for  in  these  minute  processes,  both  the  capillary  blood-vessels  and 
the  lacteals  are  brought  almost  into  contact  with  the  intestinal  contents. 
There  seems  to  be  no  doubt  that  absorption  of  fatty  matters  during  diges- 
tion, from  the  contents  of  the  intestines,  is  effected  chiefly  between  the 
epithelial  cells  which  line  the  intestinal  tract  (Watney),  and  especially 
those  which  clothe  the  surface  of  the  villi.  Thence,  the  fatty  particles 
are  passed  on  into  the  interior  of  the  lacteal  vessels  (Fig.  216,  a),  but 
how  they  pass,  and  what  laws  govern  their  so  doing,  are  not  at  present 
exactly  known. 

The  process  of  absorption  is  assisted  by  the  pressure  exercised  on  the 
contents  of  the  intestines  by  their  contractile  walls;  and  the  absorption  of 
fatty  particles  is  also  facilitated  by  the  presence  of  the  bile,  and  the  pan- 
creatic and  intestinal  secretions,  which  moisten  the  absorbing  surface. 
For  it  has  been  found  by  experiment,  that  the  passage  of  oil  through  an 
animal  membrane  is  made  much  easier  when  the  latter  is  impregnated 
with  an  alkaline  fluid. 

Absorption  by  the  Lymphatics.— The  real  source  of  the  lymph, 
and  the  mode  in  which  its  absorption  is  effected  by  the  lymphatic  vessels, 
were  long  matters  of  discussion.  But  the  problem  has  been  much  sim- 
plified by  more  accurate  knowledge  of  the  anatomical  relations  of  the 
lymphatic  capillaries.  The  lymph  is,  without  doubt,  identical  in  great 
part  with  the  liquor  sanguinis,  which,  as  before  remarked,  is  always 
exuding  from  the  blood-capillaries  into  the  interstices  of  the  tissues  in 
which  they  lie;  and  as  these  interstices  form  in  most  parts  of  the  body 
the  beginnings  of  the  lymphatics,  the  source  of  the  lymph  is  sufficiently 
obvious.  In  connection  with  this  may  be  mentioned  the  fact  that  changes 
in  the  character  of  the  lymph  correspond  very  closely  with  changes  in  the 
character  of  either  the  whole  mass  of  blood,  or  of  that  in  the  vessels  of 
the  part  from  which  the  lymph  is  exuded.  Thus  it  appears  that  the 
coagulability  of  the  lymph  is  directly  proportionate  to  that  of  the  blood; 
and  that  when  fluids  are  injected  into  the  blood-vessels  in  sufficient  qnan- 


304  HAND-BOOK    OF    PHYSIOLOGY. 

tity  to  distend   them,  the   injected  substance   may  be    almost  directly 
afterward  found  in  the  lymphatics. 

Some  other  matters  than  those  originally  contained  in  the  exuded 
liquor  sanguinis  may,  however,  find  their  way  with  it  into  the  lymphatic 
vessels.  Parts  which  having  entered  into  the  composition  of  a  tissue, 
and,  having  fulfilled  their  purpose,  require  to  be  removed,  may  not  be 
altogether  excrementitious,  but  may  admit  of  being  reorganized  and 
adapted  again  for  nutrition;  and  these  may  be  absorbed  by  the  lym- 
phatics, and  elaborated  with  the  other  contents  of  the  lymph  in  passing 
through  the  glands. 

Lymph-Hearts. — In  reptiles  and  some  birds,  an  important  auxiliary 
to  the  movement  of  the  lymph  and  chyle  is  supplied  in  certain  muscular 
sacs,  named  lymph-hearts  (Fig.  217),  and  it  has  been  shown  that  the 
caudal  heart  of  the  eel  is  a  lymph-heart  also.  The  number  and  position 
of  these  organs  vary.  In  frogs  and  toads  there  are  usually  four,  two 
anterior  and  two  posterior;  in  the  frog,  the  posterior  lymph-heart  on  each 
side  is  situated  in  the  ischiatic  region,  just  beneath  the  skin;  the  anterior 
lies  deeper,  just  over  the  transverse  process  of  the  third  vertebra.  Into 
each  of  these  cavities  several  lymphatics  open,  the  orifices  of  the  vessels 
being  guarded  by  valves,  which  prevent  the  retrograde  passage  of  the 


FIG.  217.— Lymphatic  heart  ( 9  lines  long,  4  lines  broad)  of  a  large  species  of  serpent,  the  Python, 
bivittatus.  4.  The  external  cellular  coat.  5.  The  thick  muscular  coat.  Four  muscular  columns  run 
across  its  cavity,  which  communicates  with  three  lymphatics  (1— only  one  is  seen  here),  and  with  two- 
veins  (2,  2).  6.  The  smooth  lining  membrane  of  the  cavity.  7.  A  small  appendage,  or  auricle,  the  cav- 
ity of  which  is  continuous  with  that  of  the  rest  of  the  organ  (after  E.  Weber). 

lymph.  From  each  heart  a  single  vein  proceeds  and  conveys  the  lymph 
directly  into  the  venous  system.  In  the  frog,  the  inferior  lymphatic 
heart,  on  each  side,  pours  its  lymph  into  a  branch  of  the  ischiatic  vein; 
by  the  superior,  the  lymph  is  forced  into  a  branch  of  the  jugular  vein, 
which  issues  from  its  anterior  surface,  and  which  becomes  turgid  each 
time  that  the  sac  contracts.  Blood  is  prevented  from  passing  from  the 
vein  into  the  lymphatic  heart  by  a  valve  at  its  orifice. 

The  muscular  coat  of  these  hearts  is  of  variable  thickness;  in  some 
cases  it  can  only  be  discovered  by  means  of  the  microscope;  but  in  every 
case  it  is  composed  of  striped  fibres.  The  contractions  of  the  heart  are 
rhythmical,  occurring  about  sixty  times  in  a  minute,  slowly,  and,  in  com- 
parison with  those  of  the  blood-hearts,  feebly.  The  pulsations  of  the 


ABSORPTION.  305 

cervical  pair  are  not  always  synchronous  with  those  of  the  pair  in  the 
ischiatic  region,  and  even  the  corresponding  sacs  of  opposite  sides  are  not 
always  synchronous  in  their  action. 

Unlike  the  contractions  of  the  blood-heart,  those  of  the  lymph-heart 
appear  to  be  directly  dependent  upon  a  certain  limited  portion  of  the 
spinal  cord.  For  Volkmann  found  that  so  long  as  the  portion  of  spinal 
cord  corresponding  to  the  third  vertebra  of  the  frog  was  uninjured,  the 
cervical  pair  of  lymphatic  hearts  continued  pulsating  after  all  the  rest  of 
the  spinal  cord  and  the  brain  were  destroyed;  while  destruction  of  this 
portion,  even  though  all  other  parts  of  the  nervous  centres  were  unin- 
jured, instantly  arrested  the  heart's  movements.  The  posterior,  or  ischi- 
atic, pair  of  lymph-hearts  were  found  to  be  governed,  in  like  manner,  by 
the  portion  of  spinal  cord  corresponding  to  the  eighth  vertebra.  Division 
of  the  posterior  spinal  roots  did  not  arrest  the  movements;  but  division 
of  the  anterior  roots  caused  them  to  cease  at  once. 


Absorption  by  Blood-vessels. — In  the  absorption  by  the  lym- 
phatic or  lacteal  vessels  just  described,  there  appears  something  like  the 
exercise  of  choice  in  the  materials  admitted  into  them.  But  the  absorp- 
tion by  blood-vessels  presents  no  such  appearance  of  selection  of  materials; 
rather,  it  appears,  that  every  substance,  whether  gaseous,  liquid,  or  a 
soluble,  or  minutely  divided  solid,  may  be  absorbed  by  the 
blood-vessels,  provided  it  is  capable  of  permeating  their 
walls,  and  of  mixing  with  the  blood;  and  that  of  all  such 
substances,  the  mode  and  measure  of  absorption  are  deter- 
mined solely  by  their  physical  or  chemical  properties  and 
conditions,  and  by  those  of  the  blood  and  the  walls  of  the 
blood-vessels. 

Osmosis. — The  phenomena  are,  indeed,  to  a  great  ex- 
tent, comparable  to  that  passage  of  fluids  through  mem- 
brane, which  occurs  quite  independently  of  vital  conditions, 
and  the  earliest  and  best  scientific  investigation  of  which 
was  made  by  Dutrochet.  The  instrument  which  he  employed 
in  his  experiments  was  named  an  endosmometer.  It  may  con- 
sist of  a  graduated  tube  expanded  into  an  open-mouthed  bell 
at  one  end,  over  which  a  portion  of  membrane  is  tied  (Fig. 
218).  If  now  the  bell  be  filled  with  a  solution  of  a  salt — 
say  sodium  chloride,  and  be  immersed  in  water,  the  water 
will  pass  into  the  solution,  and  part  of  the  sali  will  pass  out  FIG.  218.  En- 

.     ,  ...  dosmometer. 

into  the  water;  the  water,  however,  will  pass  into  the  solu- 
tion much  more  rapidly  than  the  salt  will  pass  out  into  the  water,  and  the 
diluted  solution  will  rise  in  the  tube.     To  this  passage  of  fluids  through 
membrane  the  term  Osmosis  is  applied. 

The  nature  of  the  membrane  used  as  a  septum,  and  its  affinity  for  the 
fluids  subjected  to  experiment,  have  an  important  influence,  as  might  be 
anticipated,  on  the  rapidity  and  duration  of  the  osmotic  current.     Thus, 
VOL.  I.— 20. 


306  HAND-BOOK    OF    PHYSIOLOGY. 

if  a  piece  of  ordinary  bladder  be  used  as  the  septum  between  water  and 
alcohol,  the  current  is  almost  solely  from  the  water  to  the  alcohol,  on 
account  of  the  much  greater  affinity  of  water  for  this  kind  of  membrane; 
while,  on  the  other  hand,  in  the  case  of  a  membrane  of  caoutchouc,  the 
•alcohol,  from  its  greater  affinity  for  this  substance,  would  pass  freely  into 
the  water. 

Osmosis  by  Blood-vessels. — Absorption  by  blood-vessels  is  the 
'consequence  of  their  walls  being,  like  the  membranous  septum  of  the 
•endosmometer,  porous  and  capable  of  imbibing  fluids,  and  of  the  blood 
feeing  so  composed  that  most  fluids  will  mingle  with  it.  The  process  of 
absorption,  in  an  instructive,  though  very  imperfect  degree,  may  be  ob- 
served in  any  portion  of  vascular  tissue  removed  from  the  body.  If  'such 
a  one  be  placed  in  a  vessel  of  water,  it  will  shortly  swell,  and  become 
heavier  and  moister,  through  the  quantity  of  water  imbibed  or  soaked 
into  it;  and  if  now,  the  blood  contained  in  any  of  its  vessels  be  let  out,  it 
will  be  found  diluted  with  water,  which  has  been  absorbed  by  the  blood- 
vessels and  mingled  with  the  blood.  The  water  round  the  piece  of  tissue 
also  will  become  blood-stained;  and  if  all  be  kept  at  perfect  rest,  the  stain 
derived  from  the  solution  of  the  coloring  matter  of  the  blood  (together 
with  which  chemistry  would  detect  some  of  the  albumen  and  other  parts 
of  the  liquor  sanguinis)  will  spread  more  widely  every  day.  The  same 
will  happen  if  the  piece  of  tissue  be  placed  in  a  saline  solution  instead  of 
water,  or  in  a  solution  of  coloring  or  odorous  matter,  either  of  which  will 
give  their  tinge  or  smell  to  the  blood,  and  receive,  in  exchange,  the  color 
of  the  blood. 

Colloids  and  Crystalloids. — Various  substances  have  been  classified 
according  to  the  degree  in  which  they  possess  the  property  of  passing, 
when  in  a  state  of  solution  in  water,  through  membrane;  those  which 
pass  freely,  inasmuch  as  they  are  usually  capable  of  crystallization,  being 
termed  crystalloids,  and  those  which  pass  with  difficulty,  on  account  of 
their,  physically,  glue-like  characters,  colloids.  (Graham.) 

This  distinction,  however,  between  colloids  and  crystalloids,  which  is 
made  the  basis  of  their  classification,  is  by  no  means  the  only  difference 
between  them.  The  colloids,  besides  the  absence  of  power  to  assume  a 
crystalline  form,  are  characterized  by  their  inertness  as  acids  or  bases,  and 
feebleness  in  all  ordinary  chemical  relations.  Examples  of  them  are 
found  in  albumin,  gelatin,  starch,  hydrated  alumina,  hydrated  silicic 
acid,  etc. ;  while  the  crystalloids  are  characterized  by  qualities  the  reverse 
of  those  just  mentioned  as  belonging  to  colloids.  Alcohol,  sugar,  and 
ordinary  saline  substances  are  examples  of  crystalloids. 

Rapidity  of  Absorption. — The  rapidity  with  which  matters  may  be 
absorbed  from  the  stomach,  probably  by  the  blood-vessels  chiefly,  and 
diffused  through  the  textures  of  the  body,  may  be  gathered  from  the  his- 
tory of  some  experiments.  From  these  it  appears  that  even  in  a  quarter 


ABSORPTION.  307 

of  an  hour  after  being  given  on  an  empty  stomach,  lithium  chloride  may 
be  diffused  into  all  the  vascular  textures  of  the  body,  and  into  some  of 
the  non-vascular,  as  the  cartilage  of  the  hip-joint,  as  well  as  into  the 
aqueous  humor  of  the  eye.  Into  the  outer  part  of  the  crystalline  lens  it 
^nay  pass  after  a  time,  varying  from  half  an  hour  to  an  hour  and  a  half. 
Lithium  carbonate,  when  taken  in  five  or  ten-grain  doses  on  an  empty 
stomach,  may  be  detected  in  the  urine  in  5  or  10  minutes;  or,  if  the 
stomach  be  full  at  the  time  of  taking  the  dose,  in  20  minutes.  It  may 
sometimes  be  detected  in  the  urine,  moreover,  for  six,  seven,  or  eight 
days.  (Bence  Jones.) 

Some  experiments  on  the  absorption  of  various  mineral  and  vegetable 
poisons,  have  brought  to  light  the  singular  fact,  that,  in  some  cases, 
absorption  takes  place  more  rapidly  from  the  rectum  than  from  the 
stomach.  Strychnia,  for  example,  when  in  solution,  produces  its  poison- 
ous effects  much  more  speedily  when  introduced  into  the  rectum  than 
into  the  stomach.  When  introduced  in  the  solid  form,  however,  it  is 
absorbed  more  rapidly  from  the  stomach  than  from  the  rectum,  doubtless 
because  of  the  greater  solvent  property  of  t}ie  secretion  of  the  former  than 
of  that  of  the  latter.  (Savory.) 

With  regard  to  the  degree  of  absorption  by  living  blood-vessels,  much 
depends  on  the  facility  with  which  the  substance  to  be  absorbed  can  pene- 
trate the  membrane  or  tissue  which  lies  between  it  and  the  blood-vessels. 
Thus,  absorption  will  hardly  take  place  through  the  epidermis,  but  is 
quick  when  the  epidermis  is  removed,  and  the  same  vessels  are  covered 
with  only  the  surface  of  the  cutis,  or  with  granulations.  In  general,  the 
absorption  through  membranes  is  in  an  inverse  proportion  to  the  thick- 
ness of  their  epithelia;  so  that  the  urinary  bladder  of  a  frog  is  traversed 
in  less  than  a  second;  and  the  absorption  of  poisons  by  the  stomach  or 
lungs  appears  sometimes  accomplished  in  an  immeasurably  small  time. 

Conditions  for  Absorption. — 1.  The  substance  to  be  absorbed  must, 
as  a  general  rule,  be  in  the  liquid  or  gaseous  state,  or,  if  a  solid,  must  be 
soluble  in  the  fluids  with  which  it  is  brought  in  contact.  Hence  the 
marks  of  tattooing,  and  the  discoloration  produced  by  silver  nitrate  taken 
internally,  remain.  Mercury  may  be  absorbed  even  in  the  metallic  state; 
and  in  that  state  may  pass  into  and  remain  in  the  blood-vessels,  or  be 
deposited  from  them;  and  such  substances  as  exceedingly  finely-divided 
charcoal,  when  taken  into  the  alimentary  canal,  have  been  found  in  the 
mesenteric  veins;  the  insoluble  materials  of  ointments  may  also  be  rubbed 
into  the  blood-vessels;  but  there  are  no  facts  to  determine  how  these 
various  substances  effect  their  passage.  Oil,  minutely  divided,  as  in  an 
emulsion,  will  pass  slowly  into  blood-vessels,  as  it  will  through  a  filter 
moistened  with  water;  and,  without  doubt,  fatty  matters  find  their  way 
into  the  blood-vessels  as  well  as  the  lymph-vessels  of  the  intestinal  canal, 
although  the  latter  seem  to  be  specially  intended  for  their  absorption. 


308  HAND-BOOK    OF    PHYSIOLOGY. 

2.  The  less  dense  the  fluid  to  be  absorbed,  the  more  speedy,  as  a  gen- 
eral rule,  is  its  absorption  by  the  living  blood-vessels.     Hence  the  rapid 
absorption  of  water  from  the  stomach;  also  of  weak  saline  solutions;  but 
with  strong  solutions,  there  appears  less  absorption  into,  than  effusion 
from,  the  blood-vessels. 

3.  The  absorption  is  the  less  rapid  the  fuller  and  tenser  the  blood-vessels 
are;  and  the  tension  may  be  so  great  as  to  hinder  altogether  the  entrance 
of  more  fluid.     Thus,  if  water  is  injected  into  a  dog's  veins  to  repletion, 
poison  is  absorbed  very  slowly;   but  when  the  tension  of  the  vessels  is 
diminished  by  bleeding,  the  poison  acts  quickly.    So,  when  cupping-glasses 
are  placed  over  a  poisoned  wound,  they  retard  the  absorption  of  the  poison 
not  only  by  diminishing  the  velocity  of  the  circulation  in  the  part,  but 
by  filling  all  its  vessels  too  full  to  admit  more. 

On  the  same  ground,  absorption  is  the  quicker  the  more  rapid  the  cir- 
culation of  the  blood;  not  because  the  fluid  to  be  absorbed  is  more  quickly 
imbibed  into  the  tissues,  or  mingled  with  the  blood,  but  because  as  fast 
as  it  enters  the  blood,  it  is  carried  away  from  the  part,  and  the  blood  being 
constantly  renewed,  is  constantly  as  fit  as  at  the  first  for  the  reception  of 
the  substance  to  be  absorbed. 


CHAPTER  X. 

ANIMAL  HEAT. 

THE  Average  Temperature  of  the  human  body  in  those  internal  parts 
which  are  most  easily  accessible,  as  the  mouth  and  rectum,  is  from  98*5° 
to  99-5°  F.  (36-9°— 37'4°  C.).  In  different  parts  of  the  external  surface 
of  the  human  body  the  temperature  varies  only  to  the  extent  of  two  or 
three  degrees  (F.),  when  all  are  alike  protected  from  cooling  influences; 
and  the  difference  which  under  these  circumstances  exists,  depends  chiefly 
upon  the  different  degrees  of  blood-supply.  In  the  arm-pit — the  most 
convenient  situation,  under  ordinary  circumstances,  for  examination  by 
the  thermometer — the  average  temperature  is  98 '6°  F.  (36 '9°  C.).  In 
different  internal  parts,  the  variation  is  one  or  two  degrees;  those  parts 
and  organs  being  warmest  which  contain  most  blood,  and  in  which  there 
occurs  the  greatest  amount  of  chemical  change,  e.g.,  the  glands  and  the 
muscles;  and  the  temperature  is  highest,  of  course,  when  they  are  most 
actively  working:  while  those  tissues  which,  subserving  only  a  mechanical 
function,  are  the  seat  of  least  active  circulation  and  chemical  change,  are 
the  coolest.  These  differences  of  temperature,  however,  are  actually  but 
slight,  on  account  of  the  provisions  which  exist  for  maintaining  uniform- 
ity of  temperature  in  different  parts. 

Circumstances  causing  Variations  in  Temperature.— The 
chief  circumstances  by  which  the  temperature  of  the  healthy  body  is  influ- 
enced are  the  following: — Age;  Sex;  Period  of  the  day;  Exercise;  Cli- 
mate and  Season;  Pood  and  Drink. 

Age. — The  average  temperature  of  the  new-born  child  is  only  about  1° 
F.  (-54°  C.)  above  that  proper  to  the  adult;  and  the  difference  becomes 
still  more  trifling  during  infancy  and  early  childhood.  The  temperature 
falls  to  the  extent  of  about  -2° — -5°  F.  from  early  infancy  to  puberty,  and 
by  about  the  same  amount  from  puberty  to  fifty  or  sixty  years  of  age.  In 
old  age  the  temperature  again  rises,  and  approaches  that  of  infancy;  but 
although  this  is  the  case,  yet  the  power  of  resisting  cold  is  less  in  them — 
exposure  to  a  low  temperature  causing  a  greater  reduction  of  heat  than  in 
young  persons. 

The  same  rapid  diminution  of  temperature  has  been  observed  to  occur 
in  the  new-born  young  of  most  carnivorous  and  rodent  animals  when  they 
are  removed  from  the  parent,  the  temperature  of  the  atmosphere  being 


310  HAND-BOOK    OF    PHYSIOLOGY. 

between  50°  and  53-5°  F.  (10°-12°  C.);  whereas  while  lying  close  to  the 
body  of  the  mother,  their  temperature  is  only  2  or  3  degrees  F.  lower 
than  hers.  The  same  law  applies  to  the  young  of  birds. 

Sex. — The  average  temperature  of  the  female  would  appear  to  be  very 
slightly  higher  than  that  of  the  male. 

Period  of  the  Day. — The  temperature  undergoes  a  gradual  alteration, 
to  the  extent  of  about  1°  to  1*5°  F.  (*54 — '8°  C.)  in  the  course  of  the  day 
and  night;  the  minimum  being  at  night  or  in  the  early  morning,  the 
maximum  late  in  the  afternoon. 

Exercise. — Active  exercise  raises  the  temperature  of  the  body  from  1° 
to  2°  F.  (-54°—  1.08°  C.).  This  may  be  partly  ascribed  to  generally  in- 
creased combustion-processes,  and  partly  to  the  fact,  that  every  muscular 
contraction  is  attended  by  the  development  of  one  or  two  degrees  of  heat 
in  the  acting  muscle;  and  that  the  heat  is  increased  according  to  the 
number  and  rapidity  of  these  contractions,  and  is  quickly  diffused  by  the 
blood  circulating  from  the  heated  muscles.  Possibly,  also,  some  heat 
may  be  generated  in  the  various  movements,  stretchings,  and  recoilings 
of  the  other  tissues,  as  the  arteries,  whose  elastic  walls,  alternately  dilated 
and  contracted,  may  give  out  some  heat,  just  as  caoutchouc  alternately 
stretched  and  recoiling  becomes  hot.  But  the  heat  thus  developed  cannot 
be  great.  The  great  apparent  increase  of  heat  during  exercise  depends, 
in  a  great  measure,  on  the  increased  circulation  and  quantity  of  blood, 
and,  therefore,  greater  heat,  in  parts  of  the  body  (as  the  skin,  and  espe- 
cially the  skin  of  the  extremities),  which,  at  the  same  time  that  they  feel 
more  acutely  than  others  any  changes  of  temperature,  are,  under  ordi- 
nary conditions,  by  some  degrees  colder  than  organs  more  centrally 
situated. 

Climate  and  Season. — The  temperature  of  the  human  body  is  the  same 
in  temperate  and  tropical  climates.  (Johnson,  Boileau,  Furnell.)  In 
summer  the  temperature  of  the  body  is  a  little  higher  than  in  winter;  the 
difference  amounting  to  about  a  third  of  a  degree  F.  (Wunderlich.) 

Food  and  Drink.  The  effect  of  a  meal  upon  the  temperature  of  a  body 
is  but  small.  A  very  slight  rise  usually  occurs.  Cold  alcoholic  drinks 
depress  the  temperature  somewhat  (-5°  to  1°  F.).  Warm  alcoholic 
drinks,  as  well  as  warm  tea  and  coffee,  raise  the  temperature  (about  -5°  F.). 

In  disease  the  temperature  of  the  body  deviates  from  the  normal  stand- 
ard to  a  greater  extent  than  would  be  anticipated  from  the  slight  effect 
of  external  conditions  during  health.  Thus,  in  some  diseases,  as  pneu- 
monia and  typhus,  it  occasionally  rises  as  high  as  106°  or  107°  F.  (41° — 
41 '6°  C.);  and  considerably  higher  temperatures  have  been  noted.  In 
Asiatic  cholera,  on  the  other  hand,  a  thermometer  placed  in  the  mouth 
may  sometimes  rise  only  to  77°  or  79°  F.  (25°— 26-2°  C.). 

The  temperature  maintained  by  Mammalia  in  an  active  state  of  life, 


ANIMAL    HEAT.  311 

according  to  the  tables  of  Tiedemann  and  Rudolph  i,  averages  101° 
(38.3°  C.).  The  extremes  recorded  by  them  were  96°  and  106°,  the  former 
in  the  narwhal,  the  latter  in  a  bat  ( Vespertilio  pipistrella).  In  Birds,  the 
average  is  as  high  as  107°  (41 -2°  C.);  the  highest  temperature,  111-25° 
(40 -2  C.);  being  in  the  small  species,  the  linnets,  etc.  Among  Reptiles, 
while  the  medium  they  were  in  was  75°  (23 '9°  C.)  their  average  tempera- 
ture was  82 -5°  (31*2°  C.).  As  a  general  rule,  their  temperature,  though 
it  falls  with  that  of  the  surrounding  medium,  is,  -in  temperate  media,  two 
or  more  degrees  higher;  and  though  it  rises  also  with  that  of  the  medium, 
yet  at  very  high  degrees  it  ceases  to  do  so,  and  remains  even  lower  than 
that  of  the  medium.  Fish  and  invertebrata  present,  as  a  general  rule,  the 
same  temperature  as  the  medium  in  which  they  live,  whether  that  be  high 
or  low;  only  among  fish,  the  tunny  tribe,  with  strong  hearts  and  red 
meat-like  muscles,  and  more  blood  than  the  average  of  fish  have,  are 
generally  7°  (3 '8°  C.)  warmer  than  the  water  around  them. 

The  difference,  therefore,  between  what  are  commonly  called  the  warm 
and  the  cold-blooded  animals,  is  not  one  of  absolutely  higher  or  lower 
temperature:  for  the  animals  which  to  us  in  a  temperate  climate  feel  cold 
(being  like  the  air  or  water,  colder  than  the  surface  of  our  bodies),  would 
in  an  external  temperature  of  100°  (37 '8°  C.)  have  nearly  the  same  tem- 
perature and  feel  hot  to  us.  The  real  difference  is  that  what  we  call 
warm-blooded  animals  (Birds  and  Mammalia),  have  a  certain  "permanent 
heat  in  all  atmospheres,"  while  the  temperature  of  the  others,  which  we 
call  cold-blooded,  is  "variable  with  every  atmosphere."  (Hunter.) 

The  power  of  maintaining  a  uniform  temperature,  which  Mammalia 
and  Birds  possess,  is  combined  with  the  want  of  power  to  endure  such 
changes  of  body  temperature  as  are  harmless  to  the  other  classes;  and 
when  their  power  of  resisting  change  of  temperature  ceases,  they  suffer 
serious  disturbance  or  die. 

Sources  and  Mode  of  Production  of  Heat  in  the  Body.— 

The  heat  which  is  produced  in  the  body  arises  from  combustion,  and  is 
due  to  the  fact  that  the  oxygen  of  the  atmosphere  taken  into  the  system 
is  combined  with  the  carbon  and  hydrogen  of  the  tissues.  Any  changes 
which  occur  in  the  protoplasm  of  the  tissues,  resulting  in  an  exhibition 
of  their  function,  is  attended  by  the  evolution  of  heat  and  also  by  the  pro- 
duction of  carbonic  acid  and  water;  and  the  more  active  the  changes, 
the  greater  the  heat  produced  and  the  greater  the  amount  of  the  carbonic 
acid  and  water  formed.  But  in  order  that  the  protoplasm  may  perform 
its  function,  the  waste  of  its  own  tissue  (destructive  metabolism),  must 
be  repaired  by  the  supply  of  food  material,  and  therefore  for  the  produc- 
tion of  heat  it  is  necessary  to  supply  food.  In  the  tissues,  therefore, 
two  processes  are  continually  going  on:  the  building  up  of  the  protoplasm 
from  the  food  (constructive  metabolism),  which  is  not  accompanied  by 
the  evolution  of  heat  but  possibly  by  the  reverse,  and  the  oxidation  of  the 
protoplastic  materials,  resulting  in  the  production  of  energy,  by  which 
heat  is  produced  and  carbonic  acid  and  water  are  evolved.  Some  heat 
will  also  be  generated  in  the  combination  of  sulphur  and  phosphorus  with 
oxygen,  but  the  amount,  thus  produced  is  but  small. 


312  HAND-BOOK    OF    PHYSIOLOGY. 

It  is  not  necessary  to  assume  that  the  combustion  processes,  which 
ultimately  issue  in  the  production  of  carbonic  acid  and  water,  are  as  sim- 
ple as  the  bare  statement  of  the  fact  might  seem  to  indicate.  But  com- 
plicated as  the  various  stages  of  combustion  may  be,  the  ultimate  result 
is  as  simple  as  in  ordinary  combustion  outside  the  body,  and  the  products 
are  the  same.  The  same  amount  of  heat  will  be  evolved  in  the  union 
of  any  given  quantities  of  carbon  and  oxygen,  and  of  hydrogen  and  oxy- 
gen, whether  the  combination  be  rapid  and  direct,  as  in  ordinary  combus- 
tion, or  slow  and  almost  imperceptible,  as  in  the  changes  which  occur  in 
the  living  body.  And  since  the  heat  thus  arising  will  be  distributed 
wherever  the  blood  is  carried,  every  part  of  the  body  will  be  heated  equally, 
or  nearly  so. 

This  theory,  that  the  maintenance  of  the  temperature  of  the  living 
body  depends  on  continual  chemical  change,  chiefly  by  oxidation,  of 
combustible  materials  existing  in  the  tissues,  has  long  been  established  by 
the  demonstration  that  the  quantity  of  carbon  and  hydrogen  which,  in 
a  given  time,  unites  in  the  body  with  oxygen,  is  sufficient  to  account  for 
the  amount  of  heat  generated  in  the  animal  within  the  same  time:  an 
amount  capable  of  maintaining  the  temperature  of  the  body  at  from  98° 
— 100°  F.  (36-8° — 37'8°  C.),  notwithstanding  a  large  loss  by  radiation  and 
evaporation. 

It  should  be  remembered  that  heat  may  be  introduced  into  the  body 
by  means  of  warm  drinks  and  foods,  and,  again,  that  it  is  possible  for  the 
preliminary  digestive  changes  to  be  accompanied  by  the  evolution  of  heat. 

Chief  Heat-producing  Tissues. — The  clfemical  changes  which 
produce  the  body-heat  appear  to  be  especially  active  in  certain  tissues: — 
(1),  In  the  Muscles,  which  form  so  large  a  part  of  the  organism.  The 
fact  that  the  manifestation  of  muscular  energy  is  always  attended  by  the 
evolution  of  heat  and  the  production  of  carbonic  acid  has  been  demon- 
strated by  actual  experiment;  and  when  not  actually  in  a  condition  of 
active  contraction,  a  metabolism,  not  so  active  but  still  actual,  goes  on, 
which  is  accompanied  by  the  manifestation  of  heat.  The  total  amount 
set  free  by  the  muscles,  therefore,  must  be  very  great;  and  it  has  been 
calculated  that  even  neglecting  the  heat  produced  by  the  quiet  metabolism 
of  muscular  tissue,  the  amount  of  heat  generated  by  muscular  activity 
supplies  the  principal  part  of  the  total  heat  produced  within  the  body. 
(2),  In  the  Secreting  glands,  and  principally  in  the  liver  as  being  the 
largest  and  most  active.  It  has  been  found  by  experiment  that  the  blood 
leaving  the  glands  is  considerably  warmer  than  that  entering  them.  The 
metabolism  in  the  glands  is  very  active,  and,  as  we  have  seen,  the  more 
active  the  metabolism  the  greater  the  heat  produced.  (3),  In  the  Brain; 
the  venous  blood  having  a  higher  temperature  than  the  arterial.  It 
must  be  remembered,  however,  that  although  the  organs  above  mentioned 
are  the  chief  heat-producing  parts  of  the  body,  all  living  tissues  contribute 


ANIMAL    HEAT.  313 

their  quota,  and  this  in  direct  proportion  to  their  activity.  The  blood 
itself  is  also  the  seat  of  metabolism,  and,  therefore,  of  the  production  of 
heat;  but  the  share  which  it  takes  in  this  respect,  apart  from  the  tissues 
in  which  it  circulates,  is  very  inconsiderable. 

Regulation  of  the  Temperature  of  the  Human  Body.— The 
average  temperature  of  the  body  is  maintained  under  different  conditions 
of  external  circumstances  by  mechanisms  which  permit  of  (1)  variation 
in  the  amount  of  heat  got  rid  of,  and  (2)  variations  in  the  amount  of  heat 
produced  or  introduced  into  the  body.  In  healthy  warm-blooded  animals 
the  loss  and  gain  of  heat  are  so  nearly  balanced  one  by  the  other  that, 
under  all  ordinary  circumstances,  a  uniform  temperature,  within  two  or 
three  degrees,  is  preserved. 

I.  Methods  of  Variation  in  the  amount  of  Heat  got  rid  of.— 
The  loss  of  heat  from  the  human  body  is  principally  regulated  by  the 
amount  lost  by  radiation  and  conduction  from  its  surface,  and  by  means 
of  the  constant  evaporation  of  water  from  the  same  part,  and  (2)  to  a 
much  less  degree  from  the  air -passages;  in  each  act  of  respiration,  heat 
is  lost  to  a  greater  or  less  extent  according  to  the  temperature  of  the 
atmosphere;  unless  indeed  the  temperature  of  the  surrounding  air  exceed 
that  of  the  blood.  We  must  remember  too  that  all  food  and  drink  which 
enter  the  body  at  a  lower  temperature  than  itself  abstract  a  small  measure 
of  heat:  while  the  urine  and  faeces  which  leave  the  body  at  about  its  own 
temperature  are  also  means  by  which  a  small  amount  is  lost. 

(a.)  Loss  of  Heat  from  the  /Surface  of  the  Body :  the  Skin. — By  far 
the  most  important  loss  of  heat  from  the  body, — probably  70  or  80  per  V  / 
cent,  of  the  whole  amount,  is  that  which  takes  place  by  radiation,  c$n-  )( 
duction,  and  evaporation  from  the  skin.  The  means  by  which  the  skin 
is  able  to  act  as  one  of  the  most  important  organs  for  regulating  the  tem- 
perature of  the  blood,  are — (1),  that  it  offers  a  large  surface  for  radiation, 
conduction,  and  evaporation;  (2),  that  it  contains  a  large  amount  of 
blood;  (3),  that  the  quantity  of  blood  contained  in  it  is  the  greater  under 
those  circumstances  which  demand  a  loss  of  heat  from  the  body,  and  vice 
/•"w?.  For  the  circumstance  which  directly  determines  the  quantity  of 
blood  in  the  skin,  is  that  which  governs  the  supply  of  blood  to  all  the 
tissues  and  organs  of  the  body,  namely,  the  power  of  the  vaso-motor  nerves 
to  cause  a  greater  or  less  tension  of  the  muscular  element  in  the  walls  of 
the  arteries,  and,  in  correspondence  with  this,  a  lessening  or  increase  of 
the  calibre  of  the  vessels,  accompanied  by  a  less  or  greater  current  of  blood. 
A  warm  or  hot  atmosphere  so  acts  on  the  nerve  fibres  of  the  skin,  as  to 
lead  them  to  cause  in  turn  a  relaxation  of  the  muscular  fibre  of  the  blood- 
vessels; and,  as  a  result,  the  skin  becomes  full-blooded,  hot,  and  sweating; 
and  much  heat  is  lost.  With  a  low  temperature,  on  the  other  hand,  the 
blood-vessels  shrink,  and  in  accordance  with  the  consequently  diminished 
blood-supply,  the  skin  becomes  pale,  and  cold,  and  dry;  and  no  doubt  a 


314  HAND-BOOK    OF    PHYSIOLOGY. 

similar  effect  may  be  produced  through  the  vaso-motor  centre  in  the 
medulla  and  spinal  cord.  Thus,  by  means  of  a  self-regulating  apparatus, 
the  skin  becomes  the  most  important  of  the  means  by  which  the  tempera- 
ture of  the  body  is  regulated. 

In  connection  with  loss  of  heat  by  the  skin,  reference  has  been  made 
to  that  which  occurs  both  by  radiation  and  conduction,  and  by  evapora- 
tion; and  the  subject  of  animal  heat  has  been  considered  almost  solely 
with  regard  to  the  ordinary  case  of  man  living  in  a  medium  colder  than 
his  body,  and  therefore  losing  heat  in  all  the  ways  mentioned.  The  im- 
portance of  the  means,  however,  adopted,  so  to  speak,  by  the  skin  for  regu- 
lating the  temperature  of  the  body,  will  depend  on  the  conditions  by 
which  it  is  surrounded;  an  inverse  proportion  existing  in  most  cases  be- 
tween the  loss  by  radiation  and  conduction  on  the  one  hand,  and  by 
evaporation  on  the  other.  Indeed,  the  small  loss  of  heat  by  evaporation 
in  cold  climates  may  go  far  to  compensate  for  the  greater  loss  by  radia- 
tion; as,  on  the  other  hand,  the  great  amount  of  fluid  evaporated  in  hot 
air  may  remove  nearly  as  much  heat  as  is  commonly  lost  by  both  radia- 
tion and  evaporation  in  ordinary  temperatures;  and  thus,  it  is  possible 
that  the  quantities  of  heat  required  for  the  maintenance  of  a  uniform 
proper  temperature  in  various  climates  and  seasons  are  not  so  different 
as  they,  at  first  thought,  seem. 

Many  examples  may  be  given  of  the  power  which  the  body  possesses  of 
resisting  the  effects  of  a  high  temperature,  in  virtue  of  evaporation  from 
the  skin.  Blagden  and  others  supported  a  temperature  varying  between 
198°— 211°  F.  (92°— 100°  C.)  in  dry  air  for  several  minutes;  and  in  a 
subsequent  experiment  he  remained  eight  minutes  in  a  temperature  of 
260°  F.  (126-5*  C.).  "The  workmen  of  Sir  F.  Chantrey  were  accustomed 
to  enter  a  furnace,  in  which  his  moulds  were  dried,  whilst  the  floor  was 
red-hot  and  a  thermometer  in  the  air  stood  at  350°  F.  (177 '8°  C.);  and 
Chabert,  the  fire-king,  was  in  the  habit  of  entering  an  oven  the  tempera- 
ture of  which  was  from  400°  to  600°  F."  (205°— 315°  C.)  (Carpenter.) 

But  such  heats  are  not  tolerable  when  the  air  is  moist  as  well  as  hot, 
so  as  to  prevent  evaporation  from  the  body.  0.  James  states,  that  in  the 
vapor  baths  of  Nero  he  was  almost  suffocated  in  a  temperature  of  112°  F. 
(44-5°  C.  ),  while  in  the  caves  of  Testaccio,  in  which  the  air  is  dry,  he 
wa,s  but  little  incommoded  by  a  temperature  of  176°  F.  (80°  C.).  In 
the  former,  evaporation  from  the  skin  was  impossible;  in  the  latter  it  was 
abundant,  and  the  layer  of  vapor  which  would  rise  from  all  the  surface 
of  the  body  would,  by  its  very  slowly  conducting  power,  defend  it  for  a 
time  from  the  full  action  of  the  external  heat. 

(The  glandular  apparatus,  by  which  secretion  of  fluid  from  the  skin  is 
effected,  will  be  considered  in  the  Section  on  the  Skin.) 

The  ways  by  which  the  skin  may  be  rendered  more  efficient  as  a  cool- 
ing-apparatus, by  exposure,  by  baths,  and  by  other  means  which  man 
instinctively  adopts  for  lowering  his  temperature  when  necessary,  are  too 
well  known  to  need  more  than  to  be  mentioned. 


ANIMAL    HEAT.  315 

Although  under  any  ordinary  circumstances,  the  external  application 
of  cold  only  temporarily  depresses  the  temperature  to  a  slight  extent,  it 
is  otherwise  in  cases  of  high  temperature  in  fever.  In  these  cases  a  tepid 
bath  may  reduce  the  temperature  several  degrees,  and  the  effect  so  pro- 
duced lasts  in  some  cases  for  many  hours. 

(b.)  Loss  of  Heat  from  the  Lungs. — As  a  means  for  lowering  the  tem- 
perature, the  lungs  and  air-passages  are  very  inferior  to  the  skin;  although, 
by  giving  heat  to  the  air  we  breathe,  they  stand  next  to  the  skin  in  im- 
portance. As  a  regulating  power,  the  inferiority  is  still  more  marked. 
The  air  which  is  expelled  from  the  lungs  leaves  the  body  at  about  the 
temperature  of  the  blood,  and  is  always  saturated  with  moisture.  No 
inverse  proportion,  therefore,  exists  between  the  loss  of  heat  by  radiation 
and  conduction  on  the  one  hand,  and  by  evaporation  on  the  other.  The 
colder  the  air,  for  example,  the  greater  will  be  the  loss  in  all  ways. 
Neither  is  the  quantity  of  blood  which  is  exposed  to  the  cooling  influence 
of  the  air  diminished  or  increased,  so  far  as  is  known,  in  accordance  with 
any  need  in  relation  to  temperature.  It  is  true  that  by  varying  the  num- 
ber and  depth  of  the  respirations,  the  quantity  of  heat  given  off  by  the 
lungs  may  be  made,  to  some  extent,  to  vary  also.  But  the  respiratory 
passages,  while  they  must  be  considered  important  means  by  which  heat 
is  lost,  are  altogether  subordinate,  in  the  power  of  regulating  the  temper- 
ature, to  the  skin. 

(c.)  By  Clothing. — The  influence  of  external  coverings  for  the  body 
must  not  be  unnoticed.  In  warm-blooded  animals,  they  are  always 
adapted,  among  other  purposes,  to  the  maintenance  of  uniform  tempera- 
ture; and  man  adapts  for  himself  such  as  are,  for  the  same  purpose,  fitted 
to  the  various  climates  to  which  he  is  exposed.  By  their  means,  and  by 
his  command  over  food  and  fire,  he  maintains  his  temperature  on  all 
accessible  parts  of  the  surface  of  the  earth. 

II.  Methods  of  Variation  in  the  amount  of  Heat  produced. 
—It  may  seem  to  have  been  assumed,  in  the  foregoing  pages,  that  the 
ojily  regulating  apparatus  for  temperature  required  by  the  human  body 
is  one  that  shall,  more  or  less,  produce  a  cooling  effect;  and  as  if  the 
amount  of  heat  produced  were  always,  therefore,  in  excess  of  that  which 
is  required.  Such  an  assumption  would  be  incorrect.  We  have  the  power 
of  regulating  the  production  of  heat,  as  well  as  its  loss. 

(«,)  By  Regulating  the  Quantity  and  Quality  of  the  Food  taken.— In 
food  we  have  a  means  for  elevating  our  temperature.  It  is  the  fuel, 
indeed,  on  which  animal  heat  ultimately  depends  altogether.  Thus, 
when  more  heat  is  wanted,  we  instinctively  take  more  food,  and  take 
such  kinds  of  it  as  are  good  for  combustion;  while  every-day  experience 
shows  the  different  power  of  resisting  cold  possessed,  respectively,  by  the 
well-fed  and  by  the  starved.  In  northern  regions,  again,  and  in  the 
colder  seasons  of  more  southern  climes,  the  quantity  of  food  consumed  is 


316  HAND-BOOK    OF    PHYSIOLOGY. 

(speaking  very  generally)  greater  than  that  consumed  by  the  same  men 
or  animals  in  opposite  conditions  of  climate  and  season.  And  the  food, 
which  appears  naturally  adapted  to  the  inhabitants  of  the  coldest 
climates,  such  as  the  several  fatty  and  oily  substances,  abounds  in  carbon 
and  hydrogen,  and  is  fitted  to  combine  with  the  large  quantities  of  oxy- 
gen which,  breathing  cold  dense  air,  they  absorb  from  their  lungs. 

(b.)  By  Exercise. — In  exercise,  we  have  an  important  means  of  raising 
the  temperature  of  our  bodies  (p.  310). 

(c.)  By  Influence  of  the  Nervous  System. — The  influence  of  the  nerv- 
ous system  in  modifying  the  production  of  heat  must  be  very  important, 
as  upon  nervous  influence  depends  the  amount  of  the  metabolism  of  the 
tissues.  The  experiments  and  observations  which  best  illustrate  it  are 
those  showing,  first,  that  when  the  supply  of  nervous  influence  to  a  part 
is  cut  oft',  the  temperature  of  that  part  falls  below  its  ordinary  degree; 
and,  secondly,  that  when  death  is  caused  by  severe  injury  to,  or  removal 
of,  the  nervous  centres,  the  temperature  of  the  body  rapidly  falls,  even 
though  artificial  respiration  be  performed,  the  circulation  maintained, 
and  to  all  appearance  the  ordinary  chemical  changes  of  the  body  be  com- 
pletely effected.  It  has  been  repeatedly  noticed,  that  after  division  of 
the  nerves  of  a  limb  its  temperature  falls;  and  this  diminution  of  heat 
has  been  remarked  still  more  plainly  in  limbs  deprived  of  nervous  influ- 
ence by  paralysis. 

With  equal  certainty,  though  less  definitely,  the  influence  of  the 
nervous  system  on  the  production  of  heat,  is  shown  in  the  rapid  and 
momentary  increase,  of  temperature,  sometimes  general,  at  other  times 
qpte  local,  which  is  observed  in  states  of  nervous  excitement;  in  the 
general  increase*of  warmth  of  the  body,  sometimes  amounting  to  perspi- 
ration, which  is. excited  by  passions  of  the  mind;  in  the  sudden  rush  of 
heat  to*  the  face,  which  is  not  a  mere  sensation;  and  in  the  equally  rapid 
diminution  of  temperature  in  the  depressing  passions.  But  none  of  these 
instances  suffice  to  prove  that  heat  is  generated  by  mere  nervous  action, 
independent  of  any  chemical  change;  all  are  explicable,  on  the  supposi- 
tion that  the  nervous  system  alters,  by  its  power  of  controlling  the  calibre 
of  the  blood-vessels,  the  quantity  of  blood  supplied  to  a  part;  while  any 
influence  which  the  nervous  system  may  have  in  the  production  of  heat, 
apart  from  this  influence  on^  the  blood-vessels,  is  an  indirect  one,  and  is 
derived,  from,  its  power  of  causing  such  nutritive  change  in  the  tissues  as 
may,  by  involving  the  necessity  of  chemical  action,  involve  the  produc- 
tion of  heat. 

Inhibitory  heat-centre. — Whether  a  centre  exists  which  regulates  the 
production  of  heat  in  warm-blooded  animals,  is  still  undecided.  Experi- 
ments have  shown  that  exposure  to  cold  at  once  increases  the  oxygen 
taken  in,  and  the  carbonic  acid  given  out,  indicating  an  increase  in  the 
activity  of  the  metabolism  of  the  tissues,  but  that  in  animals  poisoned  by 


ANIMAL    HEAT.  317 

urari,  exposure  to  cold  diminishes  both  the  metabolism  and  the  temper- 
ature, and  warm-blooded  animals  then  re-act  to  variations  of  the  ex-, 
ternal  temperature  just  in  the  same  way  as  cold-blooded.  These  experi- 
ments seem  to  suggest  that  there  is  a  centre,  to  which,  under  normal 
circumstances,  the  impression  of  cold  is  conveyed,  and  from  which  by 
efferent  nerves  impulses  pass  to  the  muscles,  whereby  an  increased  metab- 
olism is  induced,  and  so  an  increased  amount  of  heat  is  generated.  The 
centre  is  probably  situated  above  the  medulla.  Thus  in  urarized  animals, 
as  the  nerves  to  the  muscles,  the  metabolism  of  which  is  so  important 
in  the  production  of  heat,  are  paralyzed,  efferent  impulses  from  the  centre 
cannot  induce  the  necessary  metabolism  for  the  production  of  heat,  even 
though  afferent  impulses  from  the  skin,  stimulated  by  the  alteration  of 
temperature,  have  conveyed  to  it  the  necessity  of  altering  the  amount  of 
heat  to  be  produced.  The  same  effect  is  produced  when  the  medulla 
is  cut. 

Influence  of  Extreme  Heat  and  Cold. — In  connection  with  the 
regulation  of  animal  temperature,  and  its  maintenance  in  health  at  the 
normal  height,  may  be  noted  the  result  of  circumstances  too  powerful, 
either  in  raising  or  lowering  the  heat  of  the  body,  to  be  controlled  by  the 
proper  regulating  apparatus.  Walther  found  that  rabbits  and  dogs,  when 
tied  to  aboard  and  exposed  to  a  hot  sun,  reached  a  temperature  of  114-8° 
F.,  and  then  died.  Cases  of  sunstroke  furnish  us  with  several  examples 
in  the  case  of  man;  for  it  would  seem  that  here  death  ensues  chiefly  or 
solely  from  elevation  of  the  temperature.  In  many  febrile  diseases  the 
immediate  cause  of  death  appears  to  be  the  elevation  of  the  temperature 
to  a  point  inconsistent  with  the  continuance  of  life. 

The  effect  of  mere  loss  of  bodily  temperature  in  man  is  less  well  known 
than  the  effect  of  heat.  From  experiments  by  Walther,  it  appears  that 
rabbits  can  be  cooled  down  to  48°  F.  (8.9°  C.),  before  they  die,  if  arti- 
ficial respiration  be  kept  up.  Cooled  down  to  64°  F.  (17.8°  C.),  they 
cannot  recover  unless  external  warmth  be  applied  together  with  the 
employment  of  artificial  respiration.  Rabbits  not  cooled  below  77°  F. 
(25°  C.)  recover  by  external  warmth  alone. 


CHAPTER  XI. 

SECRETION. 

Secretion  is  the  process  by  which  materials  are  separated  from  the 
blood,  and  from  the  organs  in  which  they  are  formed,  for  the  purpose 
either  of  serving  some  ulterior  office  in  the  economy,  or  of  being  dis- 
charged from  the  body  as  useless  or  injurious.  In  the  former  case,  the 
separated  materials  are  termed  secretions;  in  the  latter,  they  are  termed 
excretions. 

Most  of  the  secretions  consist  of  substances  which,  probably,  do  not 
pre-exist  in  the  same  form  in  the  blood,  but  require  special  organs  and  a 
process  of  elaboration  for  their  formation,  e.g.,  the  liver  for  the  formation 
of  bile,  the  mammary  gland  for  the  formation  of  milk.  The  excretions, 
on  the  other  hand,  commonly  or  chiefly  consist  of  substances  which  exist 
ready-formed  in  the  blood,  and  are  merely  abstracted  therefrom.  If  from 
any  cause,  such  as  extensive  disease  or  extirpation  of  an  excretory  organ, 
the  separation  of  an  excretion  is  prevented,  and  an  accumulation  of  it  in 
the  blood  ensues,  it  frequently  escapes  through  other  organs,  and  may  be 
detected  in  various  fluids  of  the  body.  But  this  is  never  the  case  with 
secretions;  at  least  with  those  that  are  most  elaborated;  for  after  the 
removal  of  the  special  organs  by  which  any  of  them  is  elaborated,  it  is  no 
longer  formed.  Cases  sometimes  occur  in  which  the  secretion  continues 
to  be  formed  by  the  natural  organ,  but  not  being  able  to  escape  toward 
the  exterior,  on  account  of  some  obstruction,  is  re-absojbed  into  the  blood, 
and  afterward  discharged  from  it  by  exudation  in  other  ways;  but  these 
are  not  instances  of  true  vicarious  secretion,  and  must  not  be  thus 
regarded. 

These  circumstances,  and  their  final  destination,  are,  however,  the 
only  particulars  in  which  secretions  and  excretions  can  be  distinguished; 
for,  in  general,  the  structure  of  the  parts  engaged  in  eliminating  excre- 
tions is  as  complex  as  that  of  the  parts  concerned  in  the  formation  of 
secretions.  And  since  the  differences  of  the  two  processes  of  separation, 
corresponding  with  those  in  the  several  purposes  and  destinations  of  the 
fluids,  are  not  yet  ascertained,  it  will  be  sufficient  to  speak  in  general 
terms  of  the  process  of  separation  or  secretion. 

Every  secreting  apparatus  possesses,  as  essential  parts  of  its  structure, 
a  simple  and  almost  textureless  membrane,  named  the  primary  or  base- 


SECKETION. 


319 


ment-membrane;  certain  cells;  and  blood-vessels.  These  three  structural 
elements  are  arranged  together  in  various  ways;  but  all  the  varieties  nw^ 
be  classed  under  one  or  other  of  two  principal  divisions,  namely,  mem- 
branes and  glands. 


ORGANS  AND  TISSUES  OF  SECRETION. 

The  principal  secreting  membranes  are  (1)  the  Serous  and  Synovial 
membranes;  (2)  the  Mucous  membranes;  (3)  the  Mammary  gland;  (4) 
the  Lachrymal  gland;  and  (5)  the  Skin. 

(1)  Serous  Membranes. — The  serous  membranes  are  especially  dis- 
tinguished by  the  characters  of  the  endothelium  covering  their  free  sur- 


FIG.  219. — Section  of  synovial  membrane,    a,  endothelial  covering  of  elevations  of  the  membrane ; 
fo,  subserous  tissue  containing  fat  and  blood-vessels;  c,  ligament  covered  by  the  synovial  membrane. 

face:  it  always  consists  of  a  single  layer  of  polygonal  cells.  The  ground 
substance  of  most  serous  membranes  consists  of  connective-tissue  cor- 
puscles of  various  forms  lying  in  the  branching  spaces  which  constitute 
the  '  'lymph  canalicular  system"  (p.  292),  and  interwoven  with  bundles 
of  white  fibrous  tissue,  and  numerous  delicate  elastic  fibrillae,  together 
with  blood-vessels,  nerves,  and  lymphatics.  In  relation  to  the  process  of 
secretion,  the  layer  of  connective  tissue  serves  as  a  groundwork  for  the 
ramification  of  blood-vessels,  lymphatics,  and  nerves.  But  in  its  usual 
form  it  is  absent  in  some  instances,  as  in  the  arachnoid  covering  the 
dura  mater,  and  in  the  interior  of  the  ventricles  of  the  brain.  The 
primary  membrane  and  epithelium  are  always  present,  and  are  concerned 


320  HAND-BOOK    OF    PHYSIOLOGY. 

in  the  formation  of  the  fluid  by  which  the  free  surface  of  tne  membrane 
48  moistened. 

Serous  membranes  are  of  two  principal  kinds:  1st.  Those  which  line 
visceral  cavities, — the  arachnoid,  pericardium,  pleura?,  peritoneum,  and 
tunicas  vaginales.  2nd.  The  synovial  membranes  lining  the  joints,  and 
the  sheaths  of  tendons  and  ligaments,  with  which,  also,  are  usually  in- 
cluded the  synovial  bursce,  or  bursce  mucosce,  whether  these  be  subcutane- 
ous, or  situated  beneath  tendons  that  glide  over  bones. 

The  serous  membranes  form  closed  sacs,  and  exist  wherever  the  free 
surfaces  of  viscera  come  into  contact  with  each  other  or  lie  in  cavities 
unattached  to  surrounding  parts.  The  viscera  invested  by  a  serous  mem- 
brane are,  as  it  were,  pressed  into  the  shut  sac  which  it  forms,  carrying 
before  them  a  portion  of  the  membrane,  which  serves  as  their  investment. 
To  the  law  that  serous  membranes  form  shut  sacs,  there  is,  in  the 
human  subject,  one  exception,  viz. :  the  opening  of  the  Fallopian  tubes 
into  the  abdominal  cavity, — an  arrangement  which  exists  in  man  and  all 
Vertebrata,  with  the  exception  of  a  few  fishes. 

Functions. — The  principal  purpose  of  the  serous  and  synovial  mem- 
branes is  to  furnish  a  smooth,  moist  surface,  to  facilitate  the  movements 
of  the  invested  organ,  and  to  prevent  the  injurious  effects  of  friction. 
This  purpose  is  especially  manifested  in  joints,  in' which  free  and  exten- 
sive movements  take  place;  and  in  the  stomach  and  intestines,  which, 
from  the  varying  quantity  and  movements  of  their  contents,  are  in  almost 
constant  motion  upon  one  another  and  the  walls  of  the  abdomen. 

Serous  Fluid. — The  fluid  secreted  from  the  free  surface  of  the  serous 
membranes  is,  in  health,  rarely  more  than  sufficient  to  ensure  the  main- 
tenance of  their  moisture.  The  opposed  surfaces  of  each  serous  sac  are  at 
every  point  in  contact  with  each  other.  After  death,  a  larger  quantity 
of  fluid  is  usually  found  in  each  serous  sac;  but  this,  if  not  the  product 
of  manifest  disease,  is  probably  such  as  has  transuded  after  death,  or  in 
the  last  hours  of  life.  An  excess  of  such  fluid  in  any  of  the  serous  sacs 
constitutes  dropsy  of  the  sac. 

The  fluid  naturally  secreted  by  the  serous  membranes  appears  to  be 
identical,  in  general  and  chemical  characters,  with  the  serum  of  the 
blood,  or  with  very  dilute  liquor  saguinis.  It  is  of  a  pale  yellow  or  straw 
color,  slightly  viscid,  alkaline,  and,  on  account  of  the  presence  of  albu- 
men, coagulable  by  heat.  This  similarity  of  the  serous  fluid  to  the  liquid 
part  of  blood,  and  to  the  fluid  with  which  most  animal  tissues  are  moist- 
ened, renders  it  probable  that  it  is,  in  great  measure,  separated  by  simple 
transudation,  through  the  walls  of  the  blood-vessels.  The  probability  is 
increased  by  the  fact  that,  in  jaundice,  the  fluid  in  the  serous  sacs  is, 
equally  with  the  serum  of  the  blood,  colored  with  the  bile.  But  there  is 
reason  for  supposing  that  the  fluid  of  the  cerebral  ventricles  and  of  the 
arachnoid  sac  are  exceptions  to  this  rule;  for  they  differ  from  the  fluids 


SECRETION. 

of  the  other  serous  sacs  not  only  in  being  pellucid,  colorless,  and  of  much 
less  specific  gravity,  but  in  that  they  seldom  receive  the  tinge  of  hil* 
when  present  in  the  blood,  and  are  not  colored  by  madder,  or  other 
similar  substances  introduced  abundantly  into  the  blood. 

Synovial  Fluid:  Synovia.— It  is  also  probable  that  the  formation 
of  synovial  fluid  is  a  process  of  more  genuine  and  elaborate  secretion,  by 
means  of  the  epithelial  cells  on  the  surface  of  the  membrane,  and  espe- 
cially of  those  which  are  accumulated  on  the  edges  and  processes  of  the 
synovial  fringes;  for,  in  its  peculiar  density,  viscidity,  and  abundance  of 
albumin,  synovia  differs  alike  from  the  serum  of  blood  and  from  the  fluid 
of  any  of  the  serous  cavities. 

(2)  Mucous  Membranes. — The  mucous  membranes  line  all  those 
passages  by  which  internal  parts  communicate  with  the  exterior,  and  by 
which  either  matters  are  eliminated  from  the  body  or  foreign  substances 
taken  into  it.  They  are  soft  and  velvety,  and  extremely  vascular.  The 
external  surfaces  of  mucous  membranes  are  attached  to  various  other 
tissues;  in  the  tongue,  for  example,  to  muscle;  on  cartilaginous  parts,  to 
perichondrium;  in  the  cells  of  the  ethmoid  bone,  in  the  frontal  and 
sphenoidal  sinuses,  as  well  as  in  the  tympanum,  to  periosteum;  in  the 
intestinal  canal,  it  is  connected  with  a  firm  submucous  membrane,  which 
on  its  exterior  gives  attachment  to  the  fibres  of  the  muscular  coat.  The 
mucous  membranes  line  certain  principal  tracts — Gastro-Pulmonary  and 
Genito-Urinary;  the  former  being  subdivided  into  the  Digestive  and 
Respiratory  tracts.  1.  The  Digestive  tract  commences  in  the  cavity  of 
the  mouth,  from  which  prolongations  pass  into  the  ducts  of  the  salivary 
glands.  From  the  mouth  it  passes  through  the  fauces,  pharynx,  and 
oesophagus,  to  the  stomach,  and  is  thence  continued  along  the  whole  tract 
of  the  intestinal  canal  to  the  termination  of  the  rectum,  being  in  its 
course  arranged  in  the  various  folds  and  depressions  already  described, 
and  prolonged  into  the  ducts  of  the  intestinal  glands,  the  pancreas  and 
liver,  and 'into  the  gall-bladder.  2.  The  Respiratory  tract  includes  the 
mucous  membrane  lining  the  cavity  of  the  nose,  and  the  various  sinuses 
communicating  with  it,  the  lachrymal  canal  and  sac,  the  conjunctiva  of 
the  eye  and  eyelids,  and  the  prolongation  which  passes  along  the  Eusta- 
chian  tubes  and  lines  the  tympanum  and  the  inner  surface  of  the  mem- 
brana  tympani.  Crossing  the  pharynx,  and  lining  that  part  of  it  which 
is  above  the  soft  palate,  the  respiratory  tract  leads  into  the  glottis,  whence 
it  is  continued,  through  the  larynx  and  trachea,  to  the  bronchi  and  their 
divisions,  which  it  lines  as  far  as  the  branches  of  about  -^  of  an  inch  in 
diameter,  and  continuous  with  it  is  a  layer  of  delicate  epithelial  mem- 
brane  which  extends  into  the  pulmonary  cells.  3.  The  Genito-urinary 
tract,  wh:'ch  lines  the  whole  of  the  urinary  passages,  from  their  external 
orifice  to  the  termination  of  the  tubuli  uriniferi  of  the  kidneys,  extends 
also  into  the  organs  of  generation  in  both  sexes,  and  into  the  ducts  of  the 
VOL.  I.— 21. 


322  HAND-BOOK    OF    PHYSIOLOGY. 

glands  connected  with  them;  and  in  the  female  becomes  continuous  with 
£he  serous  membrane  of  the  abdomen  at  the  fimbrias  of  the  Fallopian  tubes. 

Structure. — Along  each  of  the  above  tracts,  and  in  different  portions 
of  each  of  them,  the  mucous  membrane  presents  certain  structural  pecu- 
liarities adapted  to  the  functions  which  each  part  has  to  discharge;  }Tet  in 
some  essential  characters  mucous  membrane  is  the  same,  from  whatever 
part  it  is  obtained.  In  all  the  principal  and  larger  parts  of  the  several 
tracts,  it  presents,  as  just  remarked,  an  external  layer  of  epithelium,  sit- 
uated upon  basement-membrane,  and  beneath  this,  a  stratum  of  vascular 
tissue  of  variable  thickness,  containing  lymphatic  vessels  and  nerves 
which  in  different  cases  presents  either  outgrowths  in  the  form  of  papillae 
and  villi,  or  depressions  or  involutions  in  the  form  of  glands.  But  in  the 
prolongations  of  the  tracts,  where  they  pass  into  gland-ducts,  these  con- 
stituents are  reduced  in  the  finest  branches  of  the  ducts  to  the  epithelium, 
the  primary  or  basement-membrane,  and  the  capillary  blood-vessels 
spread  over  the  outer  surface  of  the  latter  in  a  single  layer. 

The  primary  or  basement-membrane  is  a  thin  transparent  layer, 
simple,  homogeneous,  or  composed  of  endothelial  cells.  In  the  minuter 
divisions  of  the  mucous  membranes,  and  in  the  ducts  of  glands,  it  is  the 
layer  continuous  and  correspondent  with  this  basement-membrane  that 
forms  the  proper  walls  of  the  tubes.  The  cells  also  which,  lining  the 
larger  and  coarser  mucous  membranes,  constitute  their  epithelium,  are 
continuous  with,  and,  often  similar  to  those  which,  lining  the  gland- 
ducts,  are  called  gland-cells.  No  certain  distinction  can  be  drawn  be- 
tween the  epithelium-cells  of  mucous  membranes  and  gland-cells.  It  thus 
appears,  that  the  tissues  essential  to  the  production  of  a  secretion  are,  in 
their  simplest  form,  a  membrane,  having  on  one  surface  blood-vessels,  and 
on  the  other  a  layer  of  cells,  which  may  be  called  either  epithelium-cells 
or  gland-cells. 

Mucous  Fluid :  Mucus. — From  all  mucous  membranes  there  is 
secreted  either  from  the  surface  or  from  certain  special  glands,  or  from 
both,  a  more  or  less  viscid,  greyish,  or  semi-transparent  fluid,  of  alkaline 
reaction  and  high  specific  gravity,  named  mucus.  It  mixes  imperfectly 
with  water,  but,  rapidly  absorbing  liquid,  it  swells  considerably  when 
water  is  added.  Under  the  microscope  it  is  found  to  contain  epithelium 
and  leucocytes.  It  is  found  to  be  made  up,  chemically,  of  a  nitrogenous 
principle  called  mucin  which  forms  its  chief  bulk,  of  a  little  albumen,  of 
salts  chiefly  chlorides  and  phosphates,  and  water  with  traces  of  fats  and 
extractives. 

Secreting  Glands. — The  structure  of  the  elementary  portions  of  a 
secreting  apparatus,  namely  epithelium,  simple  membrane,  and  blood- 
vessels having  been  already  described  in  this  and  previous  chapters,  we 
may  proceed  to  consider  the  manner  in  which  they  are  arranged  to  form 
the  varieties  of  secreting  glands. 


SECRETION. 

The  secreting  glands  are  the  organs  to  which  the  function  of  seen  It  <m 
is  more  especially  ascribed;  for  they  appear  to  be  occupied  with  it  alone. 
They  present,  amid  manifold  diversities  of  form  and  composition,  a  gen- 
eral plan  of  structure,  by  which  they  are  distinguished  from  all  other 
.textures  of  the  body;  especially,  all  contain,  and  appear  constructed  with 
particular  regard  to,  the  arrangement  of  the  cells,  which,  as  already  ex- 
pressed, both  line  their  tubes  or  cavities  as  an  epithelium,  and  elaborate, 
as  secreting  cells,  the  substances  to  be  discharged  from  them.  Glands 
are  provided  also  with  lymphatic  vessels  and  nerves.  The  distribution  of 
the  former  is  not  peculiar,  and  need  not  be  here  considered.  Nerve -fibres 
are  distributed  both  to  the  blood-vessels  of  the  gland  and  to  its  ducts; 
and,  in  some  glands,  to  the  secreting  cells  also  (p.  229). 

Varieties. — 1.  The  simple  tubule,  or  tubular  gland  (A,  Fig.  220), 
examples  of  which  are  furnished  by  some  mucous  glands,  the  follicles  of 
Lieberkiihn  (Fig.  186),  and  the  tubular  glands  of  the  stomach.  These 
appear  to  be  simple  tubular  depressions  of  the  mucous  membrane,  the 
wall  of  which  is  formed  of  primary  membrane,  and  is  lined  with  secreting 
cells  arranged  as  an  epithelium.  To  the  same  class  may  be  referred  the 
elongated  and  tortuous  sudoriferous  glands. 

The  compound  tubular  glands  (D,  Fig.  220)  form  another  division. 
These  consist  of  main  gland-tubes,  which  divide  and  subdivide.  Each 
gland  may  consist  of  the  subdivisions  of  one  or  more  main-tubes.  The 
ultimate  subdivisions  of  the  tubes  are  generally  highly  convoluted. 
They  are  formed  of  a  basement-membrane,  lined  by  epithelium  of  various 
forms.  The  larger  tubes  may  have  an  outside  coating  of  fibrous,  areolar, 
or  muscular  tissue.  The  kidney,  testis,  salivary  glands,  pancreas,  Brun- 
ner's  glands  with  the  lachrymal  and  mammary  glands,  and  some  mucous 
glands  are  examples  of  this  type,  but  present  more  or  less  marked  varia- 
tions among  themselves. 

2.  The  aggregate  or  racemose  glands,  in  which  a  number  of  vesicles  or 
acini  are  arranged  in  groups  or  lobules  (c,  Fig.  220).  The  Meibomian 
follicles  are  examples  of  this  kind  of  gland. 

These  various  organs  differ  from  each  other  only  in  secondary  points 
of  structure;  such  as,  chiefly,  the  arrangement  of  their  excretory  ducts, 
the  grouping  of  the  acini  arid  lobules,  their  connection  by  areolar  tissue, 
and  supply  of  blood-vessels.  The  acini  commonly  appear  to  be  formed 
by  a  kind  of  fusion  of  the  walls  of  several  vesicles,  which  thus  combine 
to  form  one  cavity  lined  or  filled  with  secreting  cells  which  also  occupy 
recesses  from  the  main  cavity.  The  smallest  branches  of  the  gland-ducts 
sometimes  open  into  the  centres  of  these  cavities;  sometimes  the  acini 
are  clustered  round  the  extremities,  or  by  the  sides  of  the  ducts:  but, 
whatever  secondary  arrangement  there  may  be.,  all  have  the  same  essen- 
tial character  of  rounded  groups  of  vesicles  containing  gland-cells,  and 
opening  by  a  common  central  cavity  into  minute  ducts,  which  ducts  in 


324 


HAND-BOOK    OF    PHYSIOLOGY. 


the  large  glands  converge  and  unite  to  form  larger  and  larger  branches, 
and  at  length  by  one  common  trunk,  open  on  a  free  surface  of  membrane. 
Among  these  varieties  of  structure,  all  the  secreting  glands  are  alike  in 
some  essential  points,  besides  those  which  they  have  in  common  with  all 
truly  secreting  structures.  They  agree  in  presenting  a  large  extent  of 
secreting  surface  within  a  comparatively  small  space;  in  the  circumstance 


FIG.  220. — Plans  of  extension  of  secreting  membrane  by  inversion  or  recession  in  form  of  cavities. 
A,  simple  glands,  viz.  g,  straight  tube;  h,  sac;  i,  coiled  tube.  B,  multilocular  crypts;  fc,  of  tubular 
form:  I,  saccular.  C,  racemose,  or  saccular  compound  gland ;  m,  entire  gland,  showing  branched 
duct  and  lobular  structure:  n,  a  lobule,  detached  with  o,  branch  of  duct  proceeding  from  it.  D,  com- 
pound tubular  gland.  (Sharpey.) 

that  Avhile  one  end  of  the  gland-duct  opens  on  a  free  surface,  the  opposite 
end  is  always  closed,  having  no  direct  communication  with  blood-vessels, 
or  any  other  canal;  and  in  a  uniform  arrangement  of  capillary  blood- 
vessels, ramifying  and  forming  a  network  around  the  walls  and  in  the 
interstices  of  the  ducts  and  acini. 

Process  of  Secretion. — In  secretion  two  distinct  processes  are  con- 
cerned which  may  be  spoken  of  as,  1.  Physical,  and  2.  Chemical. 


SECRETION.  o25 

1.  Physical  processes. — These  are  such  as  can  be  closely  imitated  in 
the  laboratory,  inasmuch  as  they  consist  in  the  operation  of  well-known 
physical  laws:  they  are — 

(a)  Filtration,     (b)  Diffusion. 

(a)  Filtration  is  simply  the  passage  of  a  fluid  through  a  porous  mem- 
brane under  the  influence  of  pressure.     If  two  fluids  be  separated  by  a 
porous  membrane,  and  the  pressure  on  one  side  is  greater  than  on  the 
other,  it  is  evident  that  in  the  absence  of  counteracting  osmotic  influ- 
ences (see  below)  there  will  be  a  filtration  through  the  membrane  until 
the  pressure  on  the  two  sides  is  equalized.     Of  course  there  may  only 
be  fluid  on  one  side  of  the  membrane,  as,  in  the  ordinary  process  of  filter- 
ing through  blotting-paper,  and  then  the  filtration*  will  continue  as  long 
as  the  pressure  (in  this  case,  the  weight  of  the  'fluid)  is  sufficient  to  force 
it  through  the  pores  of  the  filter.     The  necessary  inequality  of  pressure 
may  be  obtained  either  by  diminishing  it  on  one  side,  as  in  the  case  of 
cupping;  or  increasing  it  on  the  other,  as  in  the  case  of  the  increased 
blood-pressure  and  consequent   increased  flow  of  urine  resulting  from 
copious  drinking.     By  filtration,  not  merely  water,  but  various  salts  in 
solution,  may  transude  from  the  blood-vessels.     It  seems  probable  that 
some  fluids,  such  as  the  secretions  of  serous  membranes,  are  simply  exu- 
dations or  oozings  (filtration)  from  the  blood-vessels,  whose  qualities  are 
determined  by  those  of  the  liquor  sanguinis,  while  the  quantities  are  liable 
to  variation,  and  are  chiefly  dependent  upon  the  blood-pressure. 

(b)  Diffusion  is  the  passage  of  fluids  through  a  moist  animal  mem- 
brane independent  of  pressure,  and  sometimes  actually  in  opposition  to 
it.     There  must  always  be  in  this  process  two  fluids  differing  in  composi- 
tion, one  or  both  possessing  an   affinity  for  the  intervening  membrane, 
and  the  fluids  capable  of  being  mixed  one  with  the  other;  the  osmotic 
current  continuing  in  each  direction  (when  both  fluids  have  an  affinity 
for  the  membrane)  until  the  chemical  composition  of  the  fluid  on  each 
side  of  the  septum  becomes  the  same. 

2.  Chemical  processes. — These  constitute  the  process  of  secretion  prop- 
erly so  called  as  distinguished  from  mere  transudation  spoken  of  above. 
In  the  chemical  process  of  secretion  various  materials  which  do  not  exist 
as  such  in  the  blood  are  elaborated  by  the  agency  of  the  gland-cells  from 
the  blood,  or,  to  speak  more  accurately,  from  the  plasma  which  exudes 
from  the  blood-vessels  into  the  interstices  of  the  gland-textures. 

The  best  evidence  for  this  view  is:  1st.  That  cells  and  nuclei  are  con- 
stituents of  all  glands,  however  diverse  their  outer  forms  and  other  char- 
acters, and  are  in  all  glands  placed  on  the  surface  or  in  the  cavity  whence 
the  secretion  is  poured.  2nd.  That  many  secretions  which  are  visible 
with  the  microscope  may  be  seen  in  the  cells  of  their  glands  before  they 
are  discharged.  Thus,  bile  may  be  often  discerned  by  its  yellow  tinge  in 
the  gland-cells  of  the  liver;  spermatozoids  in  the  cells  of  the  tubules  of 


326  HAND-BOOK    OF    PHYSIOLOGY. 

the  testicles;  granules  of  uric  acid  in  those  of  the  kidneys  (of  fish);  fatty 
particles,  like  those  of  milk,  in  the  cells  of  the  mammary  gland. 

Secreting  cells,  like  the  cells  or  other  elements  of  any  other  organ, 
appear  to  develop,  grow,  and  attain  their  individual  perfection  by  appro- 
priating nutriment  from  the  fluid  exuded  by  adjacent  blood-vessels  and 
elaborating  it,  so  that  it  shall  form  part  of  their  own  substance.  In  this 
perfected  state,  the  cells  subsist  for  some  brief  time,  and  when  that 
period  is  over  they  appear  to  dissolve,  wholly  or  in  part,  and  yield  their 
contents  to  the  peculiar  material  of  the  secretion.  And  this  appears  to  be 
the  case  in  every  part  of  the  gland  that  contains  the  appropriate  gland- 
cells;  therefore  not  in  the  extremities  of  the  ducts  or  in  the  acini  alone, 
but  in  great  part  of  their  length. 

We  have  described  elsewhere  the  changes  which  have  been  noticed 
from  actual  experiment  in  the  cells  of  the  salivary  glands,  pancreas,  and 
peptic  gland  (pp.  235,  259,  265). 

Discharge  of  Secretions  from  glands  may  either  take  place  as  soon 
as  they  are  formed;  or  the  secretion  may  be  long  retained  within  the 
gland  or  its  ducts.  The  former  is  the  case  with  the  sweat  glands.  But 
the  secretions  of  those  glands  whose  activity  of  function  is  only  occa- 
sional are  usually  retained  in  the  cells  in  an  undeveloped  form  during  the 
periods  of  the  gland's  inaction.  And  there  are  glands  which  are  like 
both  these  classes,  such  as  the  lachrymal,  which  constantly  secrete  small 
portions  of  fluid,  and  on  occasions  of  greater  excitement  discharge  it  more 
abundantly. 

When  discharged  into  the  ducts,  the  further  course  of  secretions  is 
affected  partly  by  the  pressure  from  behind;  the  fresh  quantities  of  secre- 
tion propelling  those  that  were  formed  before.  In  the  larger  ducts,  its 
propulsion  is  assisted  by  the  contraction  of  their  walls.  All  the  larger 
ducts,  such  as  the  ureter  and  common  bile-duct,  possess  in  their  coats 
plain  muscular  fibres;  they  contract  when  irritated,  and  sometimes  mani- 
fest peristaltic  movements.  Rhythmic  contractions  in  the  pancreatic  and 
bile-ducts  have  been  observed,  and  also  in  the  ureters  and  vasa  deferentia. 
It  is  probable  that  the  contractile  power  extends  along  the  ducts  to  a  con- 
siderable distance  within  the  substance  of  the  glands  whose  secretions 
can  be  rapidly  expelled.  Saliva  and  milk,  for  instance,  are  sometimes 
ejected  with  much  force;  doubtless  by  the  energetic  and  simultaneous 
contraction  of  many  of  the  ducts  of  their  respective  glands. 

Circumstances  Influencing  Secretion. — Amongst  the  principal 
conditions  which  influence  secretion  are  (1)  variations  in  the  quantity  of 
blood,  (2)  in  the  quantity  of  the  peculiar  materials  for  any  secretion  that 
it  may  contain,  and  (3)  in  conditions  of  the  nerves  of  the  glands. 

(1.)  An  increase  in  the  quantity  of  Hood  traversing  a  gland,  as  in 
nearly  all  the  instances  before  quoted,  coincides  generally  with  an  aug- 
mentation of  its  secretion.  Thus,  the  mucous  membrane  of  the  stomach 


SECRETION.  ?>'27 

becomes  florid  when,  on  the  introduction  of  food,  its  glands  begin  to 
secrete;  the  mammary  gland  becomes  much  more  vascular  during  lacta- 
tion; and  all  circumstances  which  give  rise  to  an  increase  in  the  quantity 
.of  material  secreted  by  an  organ  produce,  coincidently,  an  increased  sup- 
-ply  of  blood;  but  we  have  seen  that  a  discharge  of  saliva  may  occur  under 
extraordinary  circumstances,  without  increase  of  blood-supply  (p.  233), 
and  so  it  may  be  inferred  that  this  condition  of  increased  blood-supply 
is  not  absolutely  essential. 

(2.)  When  the  blood  contains  more  than  usual  of  the  materials  which 
the  glands  are  designed  to  separate  or  elaborate.  Thus,  when  an  excess 
of  nitrogenous  waste  is  in  the  blood,  whether  from  excessive  exercise,  or 
from  destruction  of  one  kidney,  a  healthy  kidney  will  excrete  more  urea 
than  it  did  before. 

(3.)  Influence  of  the  Nervous  System  on  Secretion. — The  process  of 
secretion  is  largely  influenced  by  the  condition  of  the  nervous  system. 
The  exact  mode  in  which  the  influence  is  exhibited  must  still  be  regarded 
as  somewhat  obscure.  In  part,  it  exerts  its  influence  by  increasing  or 
diminishing  the  quantity  of  blood  supplied  to  the  secreting  gland,  in  vir- 
tue of  the  Jiower  which  it  exercises  over  the  contractility  of  the  smaller 
blood-vessels;  while  it  also  has  a  more  direct  influence,  as  was  demon- 
strated at  length  in  the  case  of  the  submaxillary  gland,  upon  the  secreting 
cells  themselves;  this  may  be  called  trophic  influence.  Its  influence  over 
secretion,  as  well  as  over  other  functions  of  the  body,  may  be  excited  by 
causes  acting  directly  upon  the  nervous  centres,  upon  the  nerves  going 
to  the  secreting  organ,  or  upon  the  nerves  of  other  parts.  In  the  latter 
case,  a  reflex  action  is  produced:  thus  the  impression  produced  upon  the 
nervous  centres  by  the  contact  of  food  in  the  mouth,  is  reflected  upon 
the  nerves  supplying  the  salivary  glands,  and  produces,  through  these,  a 
more  abundant  secretion  of  saliva  (p.  232). 

Through  the  nerves,  various  conditions  of  the  brain  also  influence  the 
secretions.  Thus,  the  thought  of  food  may  be  sufficient  to  excite  an 
abundant  flow  of  saliva.  And,  probably,  it  is  the  mental  state  which  ex- 
cites the  abundant  secretion  of  urine  in  hysterical  paroxysms,  as  well  as 
the  perspirations  and,  occasionally,  diarrhoea,  which  ensue  under  the  influ- 
ence of  terror,  and  the  tears  excited  by  sorrow  or  excess  of  joy.  The  qual- 
ity of  a  secretion  may  also  be  affected  by  the  mind;  as  in  the  cases  in  which, 
through  grief  or  passion,  the  secretion  of  milk  is  altered,  and  is  sometimes 
so  changed  as  to  produce  irritation  in  the  alimentary  canal  of  the  child, 
or  even  death  (Carpenter). 

Relations  between  the  Secretions.— The  secretions  of  some  of 
the  glands  seem  to  bear  a  certain  relation  or  antagonism  to  each  other, 
by  which  an  increased  activity  of  one  is  usually  followed  by  diminished 
activity  of  one  oT  more  of  the  others;  and  a  deranged  condition  of  one  is 
apt  to  entail  a  disordered  state  in  the  others.  Such  relations  appear  to 


328  HAND-BOOK    OF    PHYSIOLOGY. 

exist  among  the  various  mucous  membranes;  and.  the  close  relation  be- 
tween the  secretion  of  the  kidney  and  that  of  the  skin  is  a  subject  of  con- 
stant observation. 

THE  MAMMARY  GLANDS  AND  THEIR  SECRETION: — MILK. 

Structure. — The  mammary  glands  are  composed  of  large  divisions  or 
lobes,  and  these  are  again  divisible  into  lobules, — the  lobules  being  com- 
posed of  the  convoluted  subdivision  of  ducts  (alveoli).  The  lobes  and 
lobules  are  bound  together  by  areolar  tissue;  penetrating  between  the 
lobes,  and  covering  the  general  surface  of  the  gland,  with  the  exception 
of  the  nipple,  is  a  considerable  quantity  of  yellow  fat,  itself  lobulated  by 


FIG.  221.— Dissection  of  the  lower  half  of  the  female  mamma  during  the  period  of  lactation. 
%.— In  the  left-hand  side  of  the  dissected  part  the  glandular  lobes  are  exposed  and  partially  unrav- 
eled; and  on  the  right-hand  side,  the  glandular  substance  has  been  removed  to  show  the  reticular 
loculi  of  the  connective-tissue  in  which  the  glandular  lobules  are  placed:  1,  upper  part  of  the  mainilla 
or  nipple;  2,  areola;  3,  subcutaneous  masses  of  fat;  4,  reticular  loculi  of  the  connective-tissue  which 
support  the  glandular  substance  and  contain  the  fatty  masses ;  5.  one  of  three  lactiferous  ducts  shown 
passing  toward  the  mamilla  where  they  open;  6,  one  of  the  sinus  lactei  or  reservoirs;  7,  some  of  the 
glandular  lobules  which  have  been  unraveled;  7',  others  massed  together.  (Luschka.) 

sheaths  and  processes  of  tough  areolar  tissue  (Fig.  221)  connected  both 
with  the  skin  in  front  and  the  gland  behind;  the  same  bond  of  connection 
extending  also  from  the  under  surface  of  the  gland  to  the  sheathing 
connective  tissue  of  the  great  pectoral  muscle  on  which  it  lies.  The  main 
ducts  of  the  gland,  fifteen  to  twenty  in  number,  called  the  lactiferous  or 
galactophorous  ducts,  are  formed  by  the  union  of  the  smaller  (lobular) 
ducts,  and  open  by  small  separate  orifices  through  the  nipple.  At  the 
points  of  junction  of  lobular  ducts  to  form  lactiferous  difcts,  and  just  be- 
fore these  enter  the  base  of  the  nipple,  the  ducts  are  dilated  (6,  Fig.  221); 


SECRETION.  329 

and,  during  lactation,  the  period  of  active  secretion  by  the  gland,  the 
dilatations  form  reservoirs  for  the  milk,  which  collects  in  them  and  dis- 
tends them.  The  walls  of  the  gland-ducts  are  formed  of  areolar  and  elas- 
tic with  some  muscular  tissue,  and  are  lined  internally  by  short  columnar 
•and  near  the  nipple  by  squamous  epithelium.  The  alveoli  consist  of  a 
membrana  propria  of  flattened  endothelial  cells  lined  by  low  columnar 
epithelium,  and  are  filled  with  fat  globules. 

The  nipple,  which  contains  the  terminations  of  the  lactiferous  ducts, 
is  composed  also  of  areolar  tissue,  and  contains  unstriped  muscular 
fibres.  Blood-vessels  are  also  freely  supplied  to  it,  so  as  to  give  it  a  species 
of  erectile  structure.  On  its  surface  are  very  sensitive  papillae;  and 
around  it  is  a  small  area  or  areola  of  pink  or  dark-tinted  skin,  on  which 
are  to  be  seen  small  projections  formed  by  minute  secreting  glands. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  supplied  to  the 
mammary  glands;  the  calibre  of  the  blood-vessels,  as  well  as  the  size  of 
the  glands,  varying  very  greatly  under  certain  conditions,  especially  those 
of  pregnancy  and  lactation. 

Changes  in  the  Glands  at  certain  Periods.-— The  minute 
changes  which  occur  in  the  mammary  gland  during  its  periods  of  evolu- 


FIG.  222.— Section  of  mammary  gland  of  rabbit  near  the  end  of  pregnancy,  showing  six  acini,  e, 
epithelial  cells  of  a  polyhedral  or  short  columnar  form,  with  which  the  acini  are  packed.  '  X  200. 

tion  (pregnancy),  and  involution  (when  lactation  has  ceased),  are  the  fol- 
lowing:— 

The  most  favorable  period  for  observing  the  epithelium  of  the  mam- 
mary gland  fully  developed  is  shortly  before  the  end  of  pregnancy.  At 
this  period  the  acini  which  form  the  lobules  of  the  gland,  are  found  to 
be  lined  with  a  mosaic  of  polyhedral  epithelial  cells  (Fig.  222),  and  sup- 
ported by  a  connective  tissue  stroma. 

The  rapid  formation  of  milk  during  lactation  results  from  a  fatty 
metamorphosis  of  the  epithelial  cells:  "The  secretion  may  be  said  to  be 
produced  by  a  transformation  of  the  substance  of  successive  generations 


330  HAND-BOOK    OF    PHYSIOLOGY. 

of  epithelial  cells,  and  in  the  state  of  full  activity  this  transformation  is 
so  complete  that  it  may  be  called  a  deliquescence"  (Creighton). 

In  the  earlier  days  of  lactation,  epithelial  cells  partially  transformed 
are  discharged  in  the  secretion:  these  are  termed  "colostrum  corpuscles," 
but  later  on  the  cells  are  completely  transformed  before  the  secretion  is 
discharged. 

After  the  end  of  lactation,  the  mamma  gradually  returns  to  its  original 
size  (involution).  The  acini,  in  the  early  stages  of  involution,  are  lined 
with  cells  in  all  degrees  of  vacuolation  (Fig.  223).  As  involution  proceeds 
the  acini  diminish  considerably  in  size,  and  at  length,  instead  of  a  mosaic 
of  lining  epithelial  cells  (twenty  to  thirty  in  each  acinus),  we  have  five  or  six 
nuclei  ( some  with  no  surrounding  protoplasm)  lying  in  an  irregular  heap 


FIG.  223. — Section  of  mammary  gland  of  ewe  shortly  after  the  end  of  lactation,  showing  parts  of 
four  acini,  which  contain  numerous  epithelial  cells  undergoing  vacuolation  in  situ;  they  very  closely 
resemble  young  fat-cells,  and  are  in  fact  just  like  "  Colostrum  corpuscles.11  X  300.  (Creighton.) 

within  the  acinus.  During  the  later  stages  of  involution,  large  yellow 
granular  cells  are  to  be  seen.  As  the  acini  diminish  in  size,  the  con- 
nective tissue  and  fatty  matter  between  them  increase,  and  in  some  ani- 
mals, when  the  gland  is  completely  inactive,  it  is  found  to  consist  of  a 
thin  film  of  glandular  tissue  overlying  a  thick  cushion  of  fat.  Many  of 
the  products  of  waste  are  carried  off  by  the  lymphatics. 

During  pregnancy  the  mammary  glands  undergo  changes  (evolution) 
which  are  readily  observable.  They  enlarge,  become  harder  and  more 
distinctly  tabulated:  the  veins  on  the  surface  become  more  prominent. 
The  areola  becomes  enlarged  and  dusky,  with  projecting  papillae;  the 
nipple  too  becomes  more  prominent,  and  milk  can  be  squeezed  from  the 
orifices  of  the  ducts.  This  is  a  very  gradual  process,  which  commences 
about  the  time  of  conception,  and  progresses  steadily  during  the  whole 
period  of  gestation.  The  acini  enlarge,  and  a  series  of  changes  occur, 
exactly  the  reverse  of  those  just  described  under  the  head  of  Involu- 
tion. 


SECRETION.  331 


THE  MAMMARY  SECRETION: — MILK. 

Under  tKe  microscope,  milk  is  found  to  contain  a  number  of  globules 
of  various  sizes  (Fig.  224),  the  majority  about  TTj¥FO-  of  an  inch  in  diam- 
eter. They  are  composed  of  oily  matter,  probably  coated  by  a  fine  layer 
of  albuminous  material,  and  are  called  milk-globules;  while,  accompany- 
ing these,  are  numerous  minute  particles,  both  oily  and  albuminous, 
which  exhibit  ordinary  molecular  movements.  The  milk  which  is 
secreted  in  the  first  few  days  after  parturition,  and  which  is  called  the 
rnlnsfrum,  differs  from  ordinary  milk  in  containing  a  larger  quantity  of 
solid  matter;  and  under  the  microscope  are  to  be  seen  certain  granular 


FIG.  224.— Globules  and  molecules  of  Cow's  milk.    X  400. 

masses  called  colostrum-corpuscles.  These,  which  appear  to  be  small 
masses  of  albuminous  and  oily  matter,  are  probably  secreting  cells  of  the 
gland,  either  in  a  state  of  fatty  degeneration,  or  old  cells  which  in  their 
attempt  at  secretion  under  the  new  circumstances  of  active  need  of  milk, 
are  filled  with  oily  matter;  which,  however,  being  unable  to  discharge, 
they  are  themselves  shed  bodily  to  make  room  for  their  successors.  Colos- 
trum-corpuscles have  been  seen  to  exhibit  contractile  movements  and 
to  squeeze  out  drops  of  oil  from  their  interior  (Strieker). 

Chemical  Composition. — Milk  is  in  reality  an  emulsion  consisting 
of  numberless  little  globules  of  fat,  coated  with  a  thin  layer  of  albumi- 
nous matter,  floating  in  a  large  quantity  of  water  which  contains  in  solu- 
tion casein,  serum-albumin,  milk-sugar  (lactose),  and  several  salts.  Its 
percentage  composition  has  been  already  mentioned,  but  may  be  here 
repeated.  Its  reaction  is  alkaline:  its  specific  gravity  about  1030. 


332  HAND-BOOK    OF    PHYSIOLOGY. 


TABLE  OF  THE  CHEMICAL  COMPOSITION  OF  MILK. 

Human.  Cows. 

Water 890        ...     858 

Solids  110  142 


1000  1000 
Proteids,  including  Casein  and 

Serum-Albumin      .         .                35  .         .68 

Fats  or  Butter  .         .         .         .25  .         .         .38 

Sugar  (with  extractives)     .                48  .         .30 

Salts                                                        2  6 


110  142 

When  milk  is  allowed  to  stand,  the  fat  globules,  being  the  lightest 
portion,  rise  to  the  top,  forming  cream.  If  a  little  acetic  acid  be  added 
to  a  drop  of  milk  under  the  microscope,  the  albuminous  film  coating  the 
oil  drops  is  dissolved,  and  they  run  together  into  larger  drops.  The  same 
result  is  produced  by  the  process  of  churning,  the  effect  of  which  is  to 
break  up  the  albuminous  coating  of  the  oil  drops:  they  then  coalesce  to 
form  butter. 

Curdling  of  Milk. — If  milk  be  allowed  to  stand  for  some  time,  its 
reaction  becomes  acid:  in  popular  language  it  "turns  sour/'  This  change 
appears  to  be  due  to  the  conversion  of  the  milk-sugar  into  lactic  acid, 
which  causes  the  precipitation  of  the  casein  (curdling):  the  curd  con- 
tains the  fat  globules:  the  remaining  fluid  (whey)  consists  of  water  hold- 
ing in  solution  albumin,  milk-sugar  and  certain  salts.  The  same  effect 
is  produced  in  the  manufacture  of  cheese,  which  is  really  casein  coagu- 
lated by  the  agency  of  rennet  (p.  248).  When  milk  is  boiled,  a  scum  of 
serum-albumin  forms  on  the  surface. 

Curdling  Ferments. — The  effect  of  the  ferments  of  the  gastric,  pan- 
creatic, and  intestinal  juices  in  curdling  milk  (curdling  ferments)  has 
already  been  mentioned  in  the  Chapter  on  Digestion. 

The  salts  of  milk  are  chlorides,  sulphates,  phosphates,  and  carbonates 
of  potassium,  sodium,  calcium. 


CHAPTEK  XII. 

THE  SKIN  AND  ITS  FUNCTIONS. 

THE  skin  serves — (1),  as  an  external  integument  for  the  protection  of 
the  deeper  tissues,  and  (2),  as  a  sensitive  organ  in  the  exercise  of  touch; 
it  is  also  (3),  an  important  excretory,  and  (4),  an  absorbing  organ;  while 
it  plays  an  important  part  in  (5)  the  regulation  of  the  temperature  of  the 
body. 

Structure  of  the  Skin. — The  skin  consists,  principally,  of  a  vascu- 
lar tissue,  named  the  corium,  derma,  or  cut  is  vera,  and  an  external  cover- 
ing of  epithelium  termed  the  cuticle  or  epidermis.  Within  and  beneath 
the  corium  are  imbedded  several  organs  with  special  function,  namely 
sudoriferous  glands,  sebaceous  glands,  and  hair  follicles;  and  on  its  surface 
are  sensitive  papilla.  The  so-called  appendages  of  the  skin — the  hair  and 
nails — are  modifications  of  the  epidermis. 

Epidermis. — The  epidermis  is  composed  of  several  strata  of  cells  of 
various  shapes,  and  closely  resembles  in  its  structure  that  which  lines  the 
mouth.  The  following  four  layers  may  be  distinguished.  1.  Stratum 
conieum  (Fig.  225,  «),  consisting  of  many  superposed  layers  of  horny 
scales.  The  different  thickness  of  the  epidermis  in  different  regions  of 
the  body  is  chiefly  due  to  variations  in  the  thickness  of  this  layer;  e.g., 
on  the  horny  parts  of  the  palms  of  the  hands  and  soles  of  the  feet  it  is  of 
great  thickness.  The  stratum  corneum  of  the  buccal  epithelium  chiefly 
differs  from  that  of  the  epidermis  in  the  fact  that  nuclei  are  to  be  dis- 
tinguished in  some  of  the  cells  even  of  its  most  superficial  layers. 

2.  Stratum  lucidum,  a  bright  homogeneous   membrane  consisting  of 
squamous  cells  closely  arranged,  in  some  of  which  a  nucleus  can  be  seen. 

3.  Stratum  granulosum,  consisting  of  one  layer  of  flattened  cells  which 
appear  fusiform  in  vertical  section:  they  are  distinctly  nucleated,  and  a 
number  of  granules  extend  from  the  nucleus  to  the  margins  of  the  cell. 

4.  Stratum  Malpighii  or  Rete  mucosum,  which  consists  of  many  strata, 
The  deepest  cells,  placed  immediately  above  the  ctitis  vera,  are  columnar 
with  oval  nuclei:  this  layer  of  columnar  cells  is  succeeded  by  a  number 
of  layers  of  more  or  less  polyhedral  cells  with  spherical  nuclei;  the  cells 
of  the  more  superficial  layers  are  considerably  flattened.     The  deeper  sur- 
face of  the  rete  mucosum  is  accurately  adapted  to  the  papillae  of  the 
true  skill,  being,  as  it  were,   moulded  on  them.     It  is  very  constant  in 
thickness  in  all  parts  of  the  skin.     The  cells  of  the  middle  layers  of  the 


334 


HAND-BOOK    OF    PHYSIOLOGY. 


stratum  Malpighii  are  almost  all  connected  by  processes,  and  thus  form 
"prickle  cells"  (p.  21).  The  pigment  of  the  skin,  the  varying  quantity 
of  which  causes  the  various  tints  observed  in  different  individuals  and 
different  races,  is  contained  in  the  deeper  cells  of  the  rete  mucosum;  the 
pigmented  cells  as  they  approach  the  free  surface  gradually  losing  their 
color.  Epidermis  maintains  its  thickness  in  spite  of  the  constant  wear 
and  tear  to  which  it  is  subjected.  The  columnar  cells  of  the  deepest 
layer  of  the  "rete  mucosum"  elongate,  and  their  nuclei  divide  into  two 


FIG.  225.— Vertical  section  of  the  epidermis  of  the  prepuce,  a,  stratum  corneum,  of  very  few 
layers,  the  stratum  lucidum  and  stratum  granulosum  not  being  distinctly  represented:  6,  c,  d,  and  e, 
the  layers  of  the  stratum  Malpighii,  a  certain  number  of  the  cells  in  layers  d  and  e  showing  signs  of 
segmentation;  layer  c  consists  chiefly  of  prickle  or  ridge  and  furrow  cells;  /,  basement  membrane; 
<7,  cells  in  cutis  vera.  (Cadiat.) 

FIG.  226.— Vertical  section  of  skin  of  the  negro,  a,  a.  Cutaneous  papillae,  b.  Undermost  and 
dark-colored  layer  of  oblong  vertical  epidermis-cells,  c.  Stratum  Malpighii.  d.  Superficial  layers, 
including  stratum  corneum,  stratum  lucidum,  and  stratum  granulosum,  the  last  two  not  differen- 
tiated in  figure.  X  250.  (Sharpey.) 

(Fig.  225,  e).  Lastly  the  upper  part  of  the  cell  divides  from  the  lower; 
thus  from  a  long  columnar  cell  are  produced  a  polyhedral  and  a  short 
columnar  cell:  the  latter  elongates  and  the  process  is  repeated.  The 
polyhedral  cells  thus  formed  are  pushed  up  toward  the  free  surface  by  the 
production  of  fresh  ones  beneath  them,  and  become  flattened  from  pres- 
sure: they  also  become  gradually  horny  by  evaporation  and  transforma- 
tion of  their  protoplasm  into  keratin,  till  at  last  by  rubbing  they  are 
detached  as  dry  horny  scales  at  the  free  surface.  There  is  thus  a  con- 
stant production  of  fresh  cells  in  the  deeper  layers,  and  a  constant  throw- 
ing off  of  old  ones  from  the  free  surface.  When  these  two  processes  are 
accurately  balanced,  the  epidermis  maintains  its  thickness.  When,  by 


THE    SKIN    AND    ITS    FUNCTIONS.  335 

intermittent  pressure,  a  more  active  cell-growth  is  stimulated,  the  produc- 
tioii  of  cells  exceeds  their  waste  and  the  epidermis  increases  in  thickness, 
as  we  see  in  the  horny  hands  of  the  laborer. 

The  thickness  of  the  epidermis  on  different  portions  of  the  skin  is 
directly  proportioned  to  the  friction,  pressure,  and  other  sources  of  injury 
to  which  it  is  exposed;  for  it  serves  as  well  to  protect  the  sensitive  and 
vascular  cutis  from  injury  from  without,  as  to  limit  the  evaporation  of 
fluid  from  the  blood-vessels.  The  adaptation  of  the  epidermis  to  the 
latter  purposes  may  be  well  shown  by  exposing  to  the  air  two  dead  hands 
or  feet,  t>f  which  one  has  its  epidermis  perfect,  and  the  other  is  deprived 
of  it;  in  a  day,  the  skin  of  the  latter  will  become  brown,  dry,  and  horn- 
like, while  that  of  the  former  will  almost  retain  its  natural  moisture. 

Cutis  vera.  —  The  cor  mm  or  cutis,  which  rests  upon  a  layer  of  adi- 
pose and  cellular  tissue  of  varying  thickness,  is  a  dense  and  tough,  but 
yielding  and  highly  elastic  structure,  composed  of  fasciculi  of  fibro- 
cellular  tissue,  interwoven  in  all  directions,  and  forming,  by  their  inter- 
lacements, numerous  spaces  or  areolae.  These  areolae  are  large  in  the 
deeper  layers  of  the  cutis,  and  are  there  usually  filled  with  little  masses 
of  fat  (Fig.  228):  but,  in  the  superficial  parts,  they  are  small  or  entirely 
obliterated.  Plain  muscular  fibre  is  also  abundantly  present. 

Papillae.  —  The  papillae  are  conical  elevations  of  the  cutis  vera,  with  a 
single  or  divided  free  extremity,  more  prominent  and  more  densely  set  at 
some  parts  than  at  others  (Figs.  227  and  230).  The  parts  on  which  they 
are  most  abundant  and  most  prominent,  are  the  palmar  surface  of  the 


FIG.  227.—  Compound  papillae  from  the  palm  of  the  hand;  a,  basis  of  a  papilla:  6,  6,  divisions  or 
branches  of  the  same;  c,  c,  branches  belonging  to  papillae,  of  which  the  bases  are  hidden  from  view. 
XGO.  (Kolliker.) 

hands  and  fingers,  and  the  soles  of  the  feet  —  parts,  therefore,  in  which 
the  sense  of  touch  is  most  acute.  On  these  parts  they  are  disposed  in 
double  rows,  in  parallel  curved  lines,  separated  from  each  other  by 
depressions.  Thus  they  may  be  seen  easily  on  the  palm,  whereon  each 
raised  line  is  composed  of  a  double  row  of  papillae,  and  is  intersected  by 
short  transverse  lines  or  furrows  corresponding  with  the  interspaces 
between  the  successive  pairs  of  papillae.  Over  other  parts  of  the  skin 
they  are  more  or  less  thinly  scattered,  and  are  scarcely  elevated  above  the 
surface.  Their  average  length  is  about  y^-  of  an  inch,  and  at  their  base 


336 


HAND-BOOK    OF    PHYSIOLOGY. 


they  measure  about  ^J-g-  of  an  inch  in  diameter.  Each  papilla  is  abun- 
dantly supplied  with  blood,  receiving  from  the  vascular  plexus  in  the 
cutis  one  or  more  minute  arterial  twigs,  which  divide  into  capillary  loops 
in  its  substance,  and  then  reunite  into  a  minute  vein,  which  passes  out  at 
its  base.  The  abundant  supply  of  blood  which  the  papillae  thus  receive 
explains  the  turgescence  or  kind  of  erection  which  they  undergo  when 
the  circulation  through  the  skin  is  active.  The  majority,  but  not  all,  of 


FIG.  228.— Vertical  section  of  skin.  A.  Sebaceous  gland  opening  into  hair-follicle.  B.  Muscular 
fibres.  C.  Sudoriferous  or  sweat-gland.  D.  Subcutaneous  fat.  E.  Fundus  of  hair-follicle,  with  hair- 
papillae.  (Klein  and  Noble  Smith.) 

the  papillae  contain  also  one  or  more  terminal  nerve-fibres,  from  the 
ultimate  ramifications  of  the  cutaneous  plexus,  on  which  their  exquisite 
sensibility  depends. 

Nerve-terminations. — In  some  parts,  especially  those  in  which  the 
sense  of  touch  is  highly  developed,  as,  for  example,  the  palm  of  the  hand 
and  the  lips,  the  nerve-fibres  appear  to  terminate,  in  many  of  the  papillae, 
by  one  or  more  free  ends  in  the  substance  of  an  oval-shaped  body,  occupy- 
ing the  principal  part  of  the  interior  of  the  papillae,  and  termed  a  touch- 


THE    SKIN    AND    ITS    FUNCTIONS. 


337 


corpuscle  (Fig.  229).  The  nature  of  this  body  is  obscure.  Some  regard  it 
as  little  else  than  a  mass  of  fibrous  or  connective  tissue,  surrounded  by 
elastic  fibres,  and  formed,  according  to  Huxley,  by  an  increased  develop- 
ment of  th6  primitive  sheaths  of  the  nerve-fibres,  entering  the  papillae. 
Others,  however,  believe  that,  instead  of  thus  consisting  of  a  homogeneous 
mass  of  connective  tissue,  they  are  special  and  peculiar  bodies  of  lami- 
nated structure,  directly  concerned  in  the  sense  of  touch.  They  do  not 
occur  in  all  the  papilla?  of  the  parts  where  they  are  found,  and,  as  a  rule, 
in  the  papillae  in  which  they  are  present  there  are  no  blood- vessels.  Since 


FIG.  229.— Papillae  from  the  skin  of  the  hand,  freed  from  the  cuticle  and  exhibiting  tactile  cor- 
puscles. A.  Simple  papilla  with  four  nerve-fibres:  a,  tactile  corpuscles:  6,  nerves.  B.  Papilla  treated 
with  acetic  acid;  a,  cortical  layer  with  cells  and  fine  elastic  filaments;  ft,  tactile  corpuscle  with  trans- 
verse nuclei;  c,  entering  nerve  with  neurilemma  or  perineurium ;  d,  nerve-fibres  winding  round  the 
corpuscle,  c.  Papilla  viewed  from  above  so  as  to  appear  as  a  cross-section:  a,  cortical  layer;  6,  nerve- 
fibre;  c,  sheath  of  the  tactile  corpuscle  containing  nuclei;  d,  core.  X  350.  (Kolliker.) 

these  peculiar  bodies  in  which  the  nerve-fibres  end  are  only  met  with  in 
the  papillae  of  highly  sensitive  parts,  it  may  be  inferred  that  they  are 
specially  concerned  in  the  sense  of  touch,  yet  their  absence  from  the 
papillae  of  other  tactile  parts  shows  that  they  are  not  essential  to  this 
sense. 

Closely  allied  in  structure  to  the  touch-corpuscles,  are  some  little  bodies 
called  end-lulls,  about  -g-J-g-  inch  in  diameter  (Krause).  They  are  gener- 
ally oval  or  spheroidal,  and  composed  externally  of  a  coat  of  connective 
tissue  enclosing  a  softer  matter,  in  which  the  extremity  of  a  nerve  termi- 
nates. These  bodies  have  been  found  chiefly  in  the  lips,  tongue,  palate, 
and  the  skin  of  the  glans  penis  (Fig.  230). 

Glands  of  the  Skin. — The  skin  possesses  glands  of  two  kinds:  (a) 
Sudoriferous,  or  Sweat  Glands;  (b)  Sebaceous  Glands. 

(a)  Sudoriferous,  or  Sweat  Glands. — Each  of  these  glands  consists  of  a 
small  lobular  mass,  formed  of  a  coil  of  tubular  gland-duct,  surrounded 
by  blood-vessels  and  embedded  in  the  subcutaneous  adipose  tissue  (Fig. 
228,  c.).  From  this  mass,  the  duct  ascends,  for  a  short  distance,  in  a 
spiral  manner  through  the  deeper  part  of  the  cutis,  then  passing  straight, 
VOL.  I.— 22. 


338 


HAND-BOOK    OF    PHYSIOLOGY. 


and  then  sometimes  again  becoming  spiral,  it  passes  through  the -cuticle 
and  opens  by  an  oblique  valve-like  aperture.  In  the  parts  where  the  epi- 
dermis is  thin  the  ducts  themselves  are  thinner  and  more  nearly  straight 
in  their  course  (Fig.  228).  The  duct,  which  maintains  nearly  the  same 
diameter  throughout,  is  lined  with  a  layer  of  columnar  epithelium  (Fig. 


FIG.  230.— End-bulbs  in  papillae  (magnified)  treated  with  acetic  acid.  A,  from  the  lips:  the  white 
loops  in  one  of  them  are  capillaries.  B,  from  the  tongue.  Two  end-bulbs  seen  in  the  midst  of  the 
simple  papillae:  a,  a,  nerves.  (Kolliker.) 

231)  continuous  with  the  epidermis;  while  the  part  which  passes  through 
the  epidermis  is  composed  of  the  latter  structure  only;  the  cells  which 
immediately  form  the  boundary  of  the  canal  in  this  part  being  somewhat 
differently  arranged  from  those  of  the  adjacent  cuticle. 


FIG.  231.— Glomeruli  of  sudoriferous  gland,  divided  in  various  directions,  a,  sheath  of  the  gland ; 
&,  columnar  epithelial  lining  of  gland  tube;  c,  lumen  of  tube;  d,  divided  blood-vessel-  *  loose-con- 
nective-tissue, forming  a  capsule  to  the  gland.  (Biesiadecki.) 

The  sudoriferous  glands  are  abundantly  distributed  over  the  whole  sur- 
face of  the  body;  but  are  especially  numerous,  as  well  as  very  large,  in 
the  skin  of  the  palm  of  the  hand,  and  of  the  sole  of  the  foot.  The  glands 


THE    SKIN    AND    ITS    FUNCTIONS.  339 

by  which  the  peculiar  odorous  matter  of  the  axillae  is  secreted  form  a 
nearly  complete  layer  under  the  cutis,  and  are  like  the  ordinary  sudorifer- 
ous glands,  except  in  being  larger  and  having  very  short  ducts. 

The  peculiar  bitter  yellow  substance  secreted  by  the  skin  of  the  exter- 
nal auditory  passage  is  named  cerumen,  and  the  glands  themselves  ceru- 
min ous  glands;  but  they  do  not  much  diifer  in  structure  from  the  ordi- 
nary sudoriferous  glands. 

(b)  Sebaceous  Glands. — The  sebaceous  glands  (Fig.  232),  like  the  sudo- 
riferous glands,  are  abundantly  distributed  over  most  parts  of  the  body. 
They  are  most  numerous  in  parts  largely  supplied  with  hair,  as  the  scalp 


FIG.  232.— Sebaceous  gland  from  human  skin.    (Klein  and  Noble  Smith.) 

and  face,  and  are  thickly  distributed  about  the  entrances  of  the  various 
passages  into  the  body,  as  the  anus,  nose,  lips,  and  external  ear.  They 
are  entirely  absent  from  the  palmar  surface  of  the  hand  and  the  plantar 
surfaces  of  the  feet.  They  are  minutely  lobulated  glands  composed  of  an 
aggregate  of  small  tubes  or  sacculi  filled  with  opaque  white  substances, 
like  soft  ointment.  Minute  capillary  vessels  overspread  them;  and  their 
ducts  open  either  on  the  surface  of  the  skin,  close  to  a  hair,  or,  which  is 
more  usual,  directly  into  the  follicle  of  the  hair.  In  the  latter  case,  there 
are  generally  two  or  more  glands  to  each  hair  (Fig.  228). 

Hair. — A  hair  is  produced  by  a  peculiar  growth  and  modification  of 
the  epidermis.  Externally  it  is  covered  by  a  layer  of  fine  scales  closely 
imbricated,  or  overlapping  like  the  tiles  of  a  house,  but  with  the  free 


340 


HAND-BOOK    OF   PHYSIOLOGY. 


edges  turned  upward  (Fig.  233,  A).  It  is  called  the  cuticle  of  the  hair. 
Beneath  this  is  a  much  thicker  layer  of  elongated  horny  cells,  closely 
packed  together  so  as  to  resemble  a  fibrous  structure.  This,  very  com- 


FIG.  233. — Surface  of  a  white  hair,  magnified  160  diameters.    The  wave  lines  mark  the  upper  or 
free  edges  of  the  cortical  scales.    J5,  separated  scales,  magnified  350  diameters.    (Kolliker.) 

monly,  in  the  human  subject,  occupies  the  whole  of  the  inside  of  the  hair; 

but  in  some  cases  there  is  left  a  small  central  space  filled  by  a  substance 

called  the  medulla  or  pitli,  composed  of  small 
collections  of  irregularly  shaped  cells,  contain- 
ing sometimes  pigment  granules  or  fat,  but 
mostly  air. 

The  follicle,  in  which  the  root  of  each  hair 
is  contained  (Fig.  235),  forms  a  tubular  de- 
pression from  the  surface  of  the  skin, — descend- 
ing into  the  subcutaneous  fat,  generally  to  a 
greater  depth  than  the  sudoriferous  glands,  and 
at  its  deepest  part  enlarging  in  a  bulbous  form, 
and  often  curving  from  its  previous  rectilinear 
course.  It  is  lined  throughout  by  cells  of  epi- 
thelium, continuous  with  those  of  the  epider- 
mis, and  its  walls  are  formed  of  pellucid  mem- 
brane, which  commonly,  in  the  follicles  of  the 
largest  hairs,  has  the  structure  of  vascular 
fibrous  tissue.  At  the  bottom  of  the  follicle  is 
a  small  papilla,  or  projection  of  true  skin,  and 
it  is  by  the  production  and  out-growth  of  epi- 
dermal cells  from  the  surface  of  this  papilla 
that  the  hair  is  formed.  The  inner  wall  of  the 
follicle  is  lined  by  epidermal  cells  continuous 
with  those  covering  the  general  surface  of  the 
skin;  as  if  indeed  the  follicle  had  been  formed 
by  a  simple  thrusting  in  of  the  surface  of  the 
integument  (Fig.  234).  This  epidermal  lining 
of  the  hair  follicle,  or  root-sheath  of  the  hair, 
(Kolliker.)  See  ^  composed  of  two  layers,  the  inner  one  of 


c,  knob;  d,  hair  cuticle;  e,  internal, 
and  /,  external  root-sheath;  gi,  /i, 
dermic  coat  of  follicle;  i,  papilla; 
k,  k,  ducts  of  sebaceous  glands;  I, 
corium;  m,  mucous  layer  of  epi- 
dermis; o,  upper  limit  of  internal 

X 


THE    SKIN    AND    ITS    FUNCTIONS. 


341 


which  is  so  moulded  on  the  imbricated  scaly  cuticle  of  the  hair,  that 
its  inner  surface  becomes  imbricated  also,  but  of  course  in  the  opposite 
direction.  When  a  hair  is  pulled  out,  the  inner  layer  of  the  root-sheath 
and  part  of  vthe  outer  layer  also  are  commonly  pulled  out  with  it. 

Nails. — A  nail,  like  a  hair,  is  a  peculiar  arrangement  of  epidermal 
cells,  the  undermost  of  which,  like  those  of  the  general  surface  of  the 
integument,  are  rounded  or  elongated,  while  the  superficial  are  flattened, 


FIG.  235. 


FIG. 


FIG.  235.—  Magnified  view  of  the  root  of  a  hair,    a,  stem  or  shaft  of  hair  cut  across;  6,  inner,  and 

c,  outer  layer  of  the  epidermal  lining  of  the  hair-follicle,  called  also  the  inner  and  outer  root-sheath; 

d,  dermal  or  external  coat  of  the  hair-follicle,  shown  in  part;  e,  imbricated  scales  about  to  form  a  cor- 
tical layer  on  the  surface  of  the  hair.    The  adjacent  cuticle  of  the  root-sheath  is  not  represented,  and 
the  papilla  is  hidden  in  the  lower  part  of  the  knob  where  that  is  represented  lighter.    (Kohlraush.) 

FIG.  236. — Trans'verse  section  of  a  hair  and  hair-follicle  made  below  the  opening  of  the  sebaceous 
gland,  a,  medulla  or  pith  of  the  hair;  6,  fibrous  layer  or  cortex;  c,  cuticle;  d,  Huxley's  layer,  e, 
Henle's  layer  of  internal  root-sheath;  /and  #,  layers  of  external  root-sheath,  outside  of  g  is  a  light 
layer,  or  "  glassy  membrane."  which  is  equivalent  to  the  basement  membrane;  h.  fibrous  coat  of  hair 
sac;  i,  vessels.  (Cadiat.) 

and  of  more  horny  consistence.  That  specially  modified  portion  of  the 
corium,  or  true  skin,  by  which  the  nail  is  secreted,  is  called  the  matrix. 

The  back  edge  of  the  nail,  or  the  root  as  it  is  termed,  is  received  into 
a  shallow  crescentic  groove  in  the  matrix,  white  the  front  part  is  free  and 
projects  beyond  the  extremity  of  the  digit.  T^e  intermediate  portion  of 
the  nail  rests  by  its  broad  under-surface  on  the  front  part  of  the  matrix, 
which  is  here  called  the  led  of  the  nail.  This  part  of  the  matrix  is  not 
uniformly  smooth  on  the  surface,  but  is  raised  in  the  form  of  longitudi- 
nal and  nearly  parallel  ridges  or  laminae,  on  which  are  moulded  the  epi- 
dermal cells  of  which  the  nail  is  made  up  (Fig.  237). 

The  growth  of  the  nail,  like  that  of  the  hair,  or  of  the  epidermis 


342  HAND-BOOK    OF    PHYSIOLOGY. 

generally,  is  effected  by  a  constant  production  of  cells  from  beneath  and 
behind,  to  take  the  place  of  those  which  are  worn  or  cut  away.  Inas- 
much, however,  as  the  posterior  edge  of  the  nail,  from  its  being  lodged  in 
a  groove  of  the  skin,  cannot  grow  backward,  on  additions  being  made  to 
it,  so  easily  as  it  can  pass  in  the  opposite  direction,  any  growth  at  its 
hinder  part  pushes  the  whole  forward.  At  the  same  time  fresh  cells  are 
added  to  its  under  surface,  and  thus  each  portion  of  the  nail  becomes 
gradually  thicker  as  it  moves  to  the  front,  until,  projecting  beyond  the 


FIG.  237.— Vertical  transverse  section  through  a  small  portion  of  the  nail  and  matrix  largely 
magnified.  A,  corium  of  the  nail-bed,  raised  into  ridges  or  laminae  a,  fitting  in  between  correspond- 
ing laminae  6.  of  the  nail.  B,  Malpighian,  and  C,  horny  layer  of  nail;  d,  deepest  and  vertical  cells;  e, 
upper  flattened  cells  of  Malpighian  layer.  (Kolliker.) 

surface  of  the  matrix,  it  can  receive  no  fresh  addition  from  bene/ith,  and 
is  simply  moved  forward  by  the  growth  at  its  root,  to  be  at  last  worn 
away  or  cut  off. 

FUNCTIONS  OF  THE  SKIN. 

(1.)  By  means  of  its  toughness,  flexibility  and  elasticity,  the  skin  is 
eminently  qualified  to  serve  as  the  general  integument  of  the  body,  for 
defending  the  internal  parts  from  external  violence,  and  readily  yielding 
and  adapting  itself  to  their  various  movements  and  changes  of  position. 

(2.)  The  skin  is  the  chief  organ  of  the  sense  of  touch.  Its  whole  sur- 
face is  extremely  sensitive;  but  its  tactile  properties  are  due  more  espe- 
cially to  the  abundant  papillae  with  which  it  is  studded.  (See  Chapter 
on  Special  Senses.) 

Although  destined  especially  for  the  sense  of  touch,  the  papillae  are 
not  so  placed  as  to  come  into  direct  contact  with  external  objects;  but 


THE    SKIN    AND    ITS    FUNCTIONS.  343 

like  the  rest  of  the  surface  of  the  skin,  are  covered  by  one  or  more  layers 
of  epithelium,  forming  the  cuticle  or  epidermis.  The  papilla?  adhere 
very  intimately  to  the  cuticle,  which  is  thickest  in  the  spaces  between 
them,  but  tolerably  level  on  its  outer  surface:  hence,  when  stripped  off 
from  the  cutis,  as  after  maceration,  its  internal  surface  presents  a  series 
of  pits  and  elevations  corresponding  to  the  papillae  and  their  interspaces, 
of  which  it  thus  forms  a  kind  of  mould.  Besides  affording  by  its  imper- 
meability a  check  to  undue  evaporation  from  the  skin,  and  providing  the 
sensitive  cutis  with  a  protecting  investment,  the  cuticle  is  of  service  in 
relation  to  the  sense  of  touch.  For  by  being  thickest  in  the  spaces,  be- 
tween the  papillae,  and  only  thinly  spread  over  the  summits  of  these  pro- 
cesses, it  may  serve  to  subdivide  the  sentient  surface  of  the  skin  into  a 
number  of  isolated  points,  each  of  which  is  capable  of  receiving  a  distinct 
impression  from  an  external  body.  By  covering  the  papillae  it  renders 
the  sensation  produced  by  external  bodies  more  obtuse,  and  in  this  manner 
also  is  subservient  to  touch :  for  unless  the  very  sensitive  papillae  were 
thus  defended,  the  contact  of  substances  would  give  rise  to  pain,  instead 
of  the  ordinary  impressions  of  touch.  This  is  shown  in  the  extreme  sensi- 
tiveness and  loss  of  tactile  power  in  a  part  of  the  skin  when  deprived  of 
its  epidermis.  If  the  cuticle  is  very  thick,  however,  as  on  the  heel,  touch 
becomes  imperfect,  or  is  lost. 

(3.)  The  Secretion  of  Sebaceous  Glands,  and  Hair-follicles.— 
The  secretion  of  the  sebaceous  glands  and  hair-follicles  (for  their  products 
cannot  be  separated)  consists  of  cast-off  epithelium-cells,  with  nuclei  and 
granules,  together  with  an  oily  matter,  extractive  matter,  and  stearin; 
in  certain  parts,  also,  it  is  mixed  with  a  peculiar  odorous  principle,  which 
contains  caproic,  butyric,  and  rutic  acids.  It  is,  perhaps,  nearly  similar 
in  composition  to  the  unctuous  coating,  orvernix  caseosa,  which  is  formed 
on  the  body  of  the  foetus  while  in  the  uterus,  and  which  contains  large 
quantities  of  ordinary  fat.  Its  purpose  seems  to  be  that  of  keeping  the  skin 
moist  and  supple,  and,  by  its  oily  nature,  of  both  hindering  the  evapora- 
tion from  the  surface,  and  guarding  the  skin  from  the  effects  of  the  long- 
continued  action  of  moisture.  But  while  it  thus  serves  local  purposes,  its 
removal  from  the  body  entitles  it  to  be  reckoned  among  the  excretions  of 
the  skin;  though  the  share  it  has  in  the  purifying  of  the  blood  cannot  be 
discerned. 

(4.)  The  Excretion  of  the  Skin:  the  Sweat— The  fluid  secreted 
by  the  sudoriferous  glands  is  usually  formed  s%  gradually,  that  the  watery 
portion  of  it  escapes  by  evaporation  as  fast  as  it  reaches  the  surface.  But, 
during  strong  exercise,  exposure  to  great  external  warmth,  in  some  dis- 
eases, and  when  evaporation  is  prevented,  the  secretion  becomes  more 
sensible,  and  collects  on  the  skin  in  the  form  of  drops  of  fluid. 

The  perspimfion  of  the  skin,  as  the  term  is  sometimes  employed  in 
physiology,  includes  all  that  portion  of  the  secretions  and  exudations  from 


344  HAND-BOOK    OF    PHYSIOLOGY. 

the  skin  which  passes  off  by  evaporation;  the  sweat  includes  that  which 
may  be  collected  only  in  drops  of  fluid  on  the  surface  of  the  skin.  The 
two  terms  are,  however,  most  often  used  synonymously;  and  for  distinc- 
tion, the  former  is  called  insensible  perspiration;  the  latter  sensible  per- 
spiration. The  fluids  are  the  same,  except  that  the  sweat  is  commonly 
mingled  with  various  substances  lying  on  the  surface  of  the  skin.  The 
contents  of  the  sweat  are,  in  part,  matters  capable  of  assuming  the  form 
of  vapor,  such  as  carbonic  acid  and  water,  and  in  part,  other  matters 
which  are  deposited  on  the  skin,  and  mixed  with  the  sebaceous  secretion. 


Table  of  the  Chemical  Composition  of  Sweat. 

Water 995 

Solids:— 

Organic  Acids  (formic,  acetic,  butyric,  pro- )  .^ 

pionic,  caproic,  caprylic)  j 

Salts,  chiefly  sodium  chloride        .         .         .  1  *8 

Neutral  fats  and  cholesterin  .         .         .  •? 

Extractives  (including  urea),  with  epithelium  1-6        5 

1000 

Of  these  several  substances,  however,  only  the  carbonic  acid  and  water 
need  particular  consideration. 

Watery  Vapor. — The  quantity  of  watery  vapor  excreted  from  the 
skin  is  on  an  average  between  1^-  and  2  Ib.  daily.  This  subject  has  been 
estimated  very  carefully  by  Lavoisier  and  Sequin.  The  latter  chemist 
enclosed  his  body  in  an  air-tight  bag,  with  a  mouth-piece.  The  bag 
being  closed  by  a  strong  band  above,  and  the  mouth-piece  adjusted  and 
gummed  to  the  skin  around  the  mouth,  he  was  weighed,  and  then  re- 
mained quiet  for  several  hours,  after  which  time  he  was  again  weighed. 
The  difference  in  the  two  weights  indicated  the  amount  of  loss  by  pul- 
monary exhalation.  Having  taken  off  the  air-tight  dress,  he  was  imme- 
diately weighed  again,  and  a  fourth"  time  after  a  certain  interval.  The 
difference  between  the  Wo  weights  last  ascertained  gave  the  amount  of 
the  cutaneous  and  pulmonary  exhalation  together;  by  subtracting  from 
this  the  loss  by  pulmonary  exhalation  alone,  while  he  was  in  the  air-tight 
dress,  he  ascertained  the  amount  of  cutaneous  transpiration.  During  a 
state  of  rest,  the  average  ftss  by  cutaneous  and  pulmonary  exhalation  in 
a  minute,  is  eighteen  grains, — the  minimum  eleven  grains,  the  maximum 
thirty-two  grains;  and  of  the  eighteen  grains,  eleven  pass  off  by  the  skin, 
and  seven  by  the  lungs. 

The  quantity  of  watery  vapor  lost  by  transpiration  is  of  course  influ- 
enced by  all  external  circumstances  which  affect  the  exhalation  from 
other  evaporating  surfaces,  such  as  the  temperature,  the  hygrometric 


THE    SKIN    AND    ITS    FUNCTIONS.  345 

state,  and  the  stillness  of  the  atmosphere.  But,  of  the  variations  to 
which  it  is  subject  under  the  influence  of  these  conditions,  no  calculation 
has  been  exactly  made. 

Carbonic  Acid. — The  quantity  of  carbonic  acid  exhaled  by  the  skin 
on  an  average  is  about  y^-  to  -%fa  of  that  furnished  by  the  pulmonary 
respiration. 

The  cutaneous  exhalation  is  most  abundant  in  the  lower  classes  of 
animals,  more  particularly  the  naked  Amphibia,  as  frogs  and  toads,  whose 
skin  is  thin  and  moist,  and  readily  permits  an  interchange  of  gases  be- 
tween the  blood  circulating  in  it  and  the  surrounding  atmosphere. 
Bischoff  found  that,  after  the  lungs  of  frogs  had  been  tied  and  cut  out, 
about  a  quarter  of  a  cubic  inch  of  carbonic  acid  gas  was  exhaled  by  the 
skin  in  eight  hours.  And  this  quantity  is  very  large,  when  it  is  remem- 
bered that  a  full-sized  frog  will  generate  only  about  half  a  cubic  inch  of 
carbonic  acid  by  his  lungs  and  skin  together  in  six  hours.  (Milne- 
Edwards  and  M tiller.) 

The  importance  of  the  respiratory  function  of  the  skin,  which  was 
once  thought  to  be  proved  by  the  speedy  death  of  animals  whose  skins, 
after  removal  of  the  hair,  were  covered  with  an  impermeable  varnish,  has 
been  shown  by  further  observations  to  have  no  foundation  in  fact;  the 
immediate  cause  of  death  in  such  cases  being  the  loss  of  temperature.  A 
varnished  animal  is  said  to  have  suffered  no  harm  when  surrounded  by 
cotton  wadding,  and  to  have  died  when  the  wadding  was  removed. 

Influence  of  the  Nervous  System  on  Excretion. — Any  increase 
in  the  amount  of  sweat  secreted  is  usually  accompanied  by  dilatation  of 
the  cutaneous  vessels.  It  is,  however,  probable  that  the  secretion  is  like 
the  other  secretions,  e.g.,  the  saliva,  under  the  direct  action  of  a  special 
nervous  apparatus,  in  that  various  nerves  contain  fibres  which  act  directly 
upon  the  cells  of  the  sweat  glands  in  the  same  way  that  the  chorda  tym- 
pani  contains  fibres  which  act  directly  upon  the  salivary  cells.  The  nerve 
fibres  which  induce  sweating  may  act  independently  of  the  vaso-motor 
fibres,  whether  vaso-dilator  or  vaso-constrictor.  The  local  apparatus  is 
under  control  of  the  central  nervous  system — sweat  centres  probably  ex- 
isting both  in  the  medulla  and  spinal  cord — and  may  be  reflexly  as  well  as 
directly  excited.  This  will  explain  the  fact  that  sweat  occurs  not  only 
when  the  skfti  is  red,  but  also  when  it  is  pale,  and  the  cutaneous  circula- 
tion languid,  as  in  the  sweat  which  accompanies  syncope  or  fainting,  or 
which  immediately  precedes  death. 

(5.)  Absorption  by  the  Skin.— Absorption  by  the  skin  has  been 
already  mentioned,  as  an  instance  in  which  that  process  is  most  actively 
accomplished.  Metallic  preparations  rubbed  into  the  skin  have  the  same 
action  as  when  given  internally,  only  in  a  less  degree.  Mercury  applied 
in  this  manner  exerts  its  specific  influence  upon  syphilis,  and  excites  sali- 
vation; potassio-tartrate  of  antimony  may  excite  vomiting,  or  an  eruption 
extending  over  the  whole  body;  and  arsenic  may  produce  poisonous 


346  HAND-BOOK    OF    PHYSIOLOGY. 

effects.  Vegetable  matters,  also,  if  soluble,  or  already  in  solution,  give 
rise  to  their  peculiar  effects,  as  cathartics,  narcotics,  and  the  like,  when 
rubbed  into  the  skin.  The  effect  of  rubbing  is  probably  to  convey  the 
particles  of  the  matter  into  the  orifices  of  the  glands,  whence  they  are 
more  readily  absorbed  than  they  would  be  through  the  epidermis.  When 
simply  left  in  contact  with  the  skin,  substances,  unless  in  a  fluid  state, 
are  seldom  absorbed. 

It  has  long  been  a  contested  question  whether  the  skin  covered  with 
the  epidermis  has  the  power  of  absorbing  water;  and  it  is  a  point  the 
more  difficult  to  determine  because  the  skin  loses  water  by  evaporation. 
But,  from  the  result  of  many  experiments,  it  may  now  be  regarded  as  a 
wrell-ascertained  fact  that  such  absorption  really  occurs.  The  absorption 
of  water  by  the  surface  of  the  body  may  take  place  in  the  lower  animals 
very  raj)idly.  Not  only  frogs,  which  have  a  thin  skin,  but  lizards,  in 
which  the  cuticle  is  thicker  than  in  man,  after  having  lost  weight  by 
being  kept  for  some  time  in  a  dry  atmosphere,  were  found  to  recover  both 
their  weight  and  plumpness  very  rapidly  when  immersed  in  water.  When 
merely  the  tail,  posterior  extremities,  and  posterior  part  of  the  body  of 
the  lizard  were  immersed,  the  water  absorbed  was  distributed  throughout 
the  system.  And  a  like  absorption  through  the  skin,  though  to  a  less 
extent,  may  take  place  also  in  man. 

In  severe  cases  of  dysphagia,  when  not  even  fluids  can  be  taken  into 
the  stomach,  immersion  in  a  bath  of  warm  water  or  of  milk  and  water 
may  assuage  the  thirst;  and  it  has  been  found  in  such  cases  that  the 
weight  of  the  body  is  increased  by  the  immersion.  Sailors  also,  when 
destitute  of  fresh  water,  find  their  urgent  thirst  allayed  by  soaking  their 
clothes  in  salt  water  and  wearing  them  in  that  state;  but  these  effects  are 
in  part  due  to  the  hindrance  to  the  evaporation  of  water  from  the  skin. 

(6.)  Regulation  of  Temperature. — For  an  account  of  this  impor- 
tant function  of  the  skin,  see  Chapter  on  Animal  Heat. 


CHAPTER  XIII. 

THE  KIDNEYS  AND  THE  EXCRETION  OF  URINE. 

THE  Kidneys  are  two  in  number,  and  are  situated  deeply  in  the  lum- 
bar region  of  the  abdomen,  on  either  side  of  the  spinal  column,  behind 
the  peritoneum.  They  correspond  in  position  to  the  last  two  dorsal  and 
two  upper  lumbar  vertebrae;  the  right  being  slightly  lower  than  the  left 
in  consequence  of  the  position  of  the  liver  on  the  right  side  of  the  abdo- 
men. They  are  characteristic  in  shape,  about  4  inches  long,  2%  inches 
broad,  and  1-J-  inch  thick.  The  weight  of  each  kidney  is  about  4|  oz. 


FIG.  238.— Plan  of  a  longitudinal  section  through  the  pelvis  and  substance  of  the  right  kidney.  U; 
a,  the  cortical  substance:  6,  6,  broad  part  of  the  pyramids  of  Malpighii:  c,  c,  the  divisions  of  the  pel- 
vis named  calyces,  laid  open;  c'.  one  of  those  unopened;  d,  summit  of  the  pyramids  of  papillae  pro- 
jecting into  calyces:  e,  e,  section  of  the  narrow  part  of  two  pyramids  near  the  calyces:  p,  pelvis  or 
enlarged  divisions  of  the  ureter  within  the  kidney;  it,  the  ureter;  s,  the  sinus;  h,  the  hilus. 

Structure  of  the  Kidneys.— The  kidney  is  covered  by  a  rather 
tougk  fibrous  capsule,  which  is  slightly  attached  by  it's  inner  surface  to 
the  proper  substance  of  the  organ  by  means  of  very  fine  fibres  of  areolar 
tissue  and  minute  blood-vessels.  From  the  healthy  kidney,  therefore,  it 
may  be  easily  torn  off  without  injury  to  the  subjacent  cortical  portion  of 
the  organ.  At  the  hilus  or  notch  of  the  kidney,  it  becomes  continuous 
with  the  external  coat  of  the  upper  and  dilated  part  of  the  ureter  (Fig. 
238). 


348 


HAND-BOOK    OF    PHYSIOLOGY. 


On  making  a  section  lengthwise  through  the  kidney  (Fig.  238)  the 
main  part  of  its  substance  is  seen  to  be  composed  of  two  chief  portions, 
called  respectively  the  cortical  and  the  medullary  portion,  the  latter  being 
also  sometimes  called  the  pyramidal  portion,  from  the  fact  of  its  being 
composed  of  about  a  dozen  conical  bundles  of  urine-tube,  each  bundle 
being  called  a  pyramid.  The  upper  part  of  the  duct  of  the  organ,  or  the 
ureter,  is  dilated  into  what  is  called  the  pelvis  of  the  kidney;  and  this, 
again,  after  separating  into  two  or  three  principal  divisions,  is  finally  sub- 
divided into  still  smaller  portions,  varying  in  number  from  about  8  to  12, 
or  even  more,  and  called  calyces.  Each  of  these  little  calyces  or  cups, 
which  are  often  arranged  in  a  double  row,  receives  the  pointed  extremity 
or  papilla  of  a  pyramid.  Sometimes,  however,  more  than  one  papilla  is 
received  by  a  calyx. 

The  kidney  is  a  compound  tubular  gland,  and  both  its  cortical  and 
medullary  portions  are  composed  essentially  of  secreting  tubes,  the  tuliili 
uriniferi,  which,  by  one  extremity,  in  the  cortical  portion,  end  commonly 
in  little  saccules  containing  blood-vessels,  called  Malpigliian  bodies,  and, 
by  the  other,  open  through  the  papillae  into  the  pelvis  of  the  kidney,  and 
thus  discharge  the  urine  which  flows  through  them. 


FIG.  239.— A.  Portion  of  a  secreting  tubule  from  the  cortical  substance  of  the  kidnej'.    B.  The  epi- 
thelial or  gland-cells.    X  700  times. 

In  the  pyramids  the  tubes  are  chiefly  straight— dividing  and  diverg- 
ing as  they  ascend  through  these  into  the  cortical  portion;  while  in  the 
latter  region  they  spread  out  more  irregularly,  and  become  much  branched 
and  convoluted. 

Tubuli  Uriniferi. — The  tubuli  uriniferi  (Fig.  239)  are  composed  of 
a  nearly  homogeneous  membrane,  and  are  lined  internally  by  epithelium. 
They  vary  considerably  in  size  in  different  parts  of  their  course,  but  are, 
on  an  average,  about  -g-}-^  of  an  inch  in  diameter,  and  are  found  to  be 


THE    KIDNEYS    AND    URINE. 


349 


made  up  of  several  distinct  sections  which  differ  from  one  another  MTV 
markedly,  both  in  situation  and  structure.  According  to  Klein,  the  fol- 
lowing segments  maybe  made  out:  (1)  The  Malpighian  corpuscle  (Figs. 


FIG.  240.—  A  Diagram  of  the  sections  of  uriniferous  tubes.    A,  Cortex  limited  externally  by  the 
capsule : 
without  Mali 

tubule  of  Schachowa*  5.  descending  lirnb  of  Henle's  loop:  6,  the  loop  proper;  7,  thick  part  of  the  as- 
cending limb;  8.  spiral  part  of  ascending  limb;  9,  narrow  ascending  limb  in  the  medullary  ray;  10, 
the  irregular  tubule;  11.  the  intercalated  .section  of  Schweigger-Seidei,  or  the  distal  convoluted  tubule; 
12,  the  curved  collecting  tubule:  13,  the  straight  collecting  tubule  of  the  medullary  ray:  14.  the  col- 
lecting tube  of  the  boundary  layer;  15.  the  large  collecting  tube  of  the  papillary  part  which,  joining 
with  similar  tubes,  forms  the  duct.  (Klein  and  Noble  Smith.) 


240,  241),  composed  of  a  hyaline  membrana  propria,  thickened  by  a  vary- 
ing amount  of  fibrous  tissue,  and  lined  by  flattened  nucleated  epithelial 


350 


HAND-BOOK    OF    PHYSIOLOGY. 


plates.  This  capsule  is  the  dilated  extremity  of  the  uriniferous  tubule, 
and  contains  within  it  a  glomerulus  of  convoluted  capillary  blood-vessels 
supported  by  connective  tissue,  and  covered  by  flattened  epithelial  plates. 
The  glomerulus  is  connected  with  an  efferent  and  an  afferent  vessel.  (2) 
The  constricted  neck  of  the  capsule  (Fig.  240,  2),  lined  in  a  similar  man- 
ner, connects  it  with  (3)  The  Proximal  convoluted  tubule,  which  forms 
several  distinct  curves  and  is  lined  with  short  columnar  cells,  which  vary 
somewhat  in  size.  The  tube  next  passes  almost  vertically  downward, 
forming  (4)  The  Spiral  tubule,  which  is  of  much  the  same  diameter,  and 


FIG.  241.— From  a  vertical  section  through  the  kidney  of  a  dog— the  capsule  of  which  is  supposed 
to  be  on  the  right,  a.  The  capillaries  of  the  Malpighian  corpuscle — viz.,  the  glomerulus,  are  arranged 
in  lobules;  n,  neck  of  capsule;  c,  convoluted  tubes  cut  in  various  directions:  6,  irregular  tubule;  d,  e, 
and /,  are  straight  tubes  running  toward  capsules  forming  a  so-called  medullary  ray;  d,  collecting 
tube;  e,  spiral  tube;  /,  narrow  section  of  ascending  limb.  X  380.  (Klein  and  Noble  Smith.) 

is  lined  in  the  same  way  as  the  convoluted  portion.  So  far  the  tube  has 
been  contained  in  the  cortex  of  the  kidney,  it  now  passes  vertically  down- 
ward through  the  most  external  part  (boundary  layer)  of  the  Malpighian 
pyramid  into  the  more  internal  part  (papillary  layer),  where  it  curves  up 
sharply,  forming  altogether  the  (  5  and  6)  Loop  of  Henle,  which  is  a  very 
narrow  tube  lined  with  flattened  nucleated  cells.  Passing  vertically  up- 
ward just  as  the  tube  reaches  the  boundary  layer  (7)  it  suddenly  enlarges 
and  becomes  lined  with  polyhedral  cells.  (8)  About  midway  in  the  boun- 
dary layer  the  tube  again  narrows,  forming  the  ascending  spiral  of 
Henle's  loop,  but  is  still  lined  with  polyhedral  cells.  At  the  point  where 
the  tube  enters  the  cortex  (9)  the  ascending  limb  narrows,  but  the  diame- 


THE    KIDNEYS    AND    URINE. 


351 


ter  varies  considerably;  here  and  there  the  cells  are  more  flattened,  but 
both  in  this  as  in  (8)  the  cells  are  in  many  places  very  angular,  branched, 
and  imbricated.  It  then  joins  (10)  the  "irregular  tubule"  which  has  a 
very  irregular  and  angular  outline,  and  is  lined  with  angular  and  imbri- 
cated cells.  The  tube  next  becomes  convoluted,  (11)  forming  the  dixfal 
convoluted  tube  or  intercalated  section  of  Schiveigger-Seidel,  which  is 
identical  in  all  respects  with  the  proximal  convoluted  tube  (12  and  13). 
The  curved  and  straight  collecting  tubes,  the  former  entering  the  latter 
at  right  angles,  and  the  latter  passing  vertically  downward,  are  lined  with 
polyhedral,  or  spindle-shaped,  or  flattened,  or  angular  cells.  The  straight 
collecting  tube  now  enters  the  boundary  layer  (14),  and  passes  on  to  the 


OTfc 


FIG.  242. 


FIG.  243. 


FIG.  242.— Transverse  section  of  a  renal  papilla;  a,  larger  tubes  or  papillary  ducts:  6,  smaller 
tubes  of  Henle:  c,  blood-vessels,  distinguished  by  their  flatter  epithelium;  d,  nuclei  of  the  stroma. 
(Kolliker.)  x  300. 

FIG.  243.— Diagram  showing  the  relation  of  the  Malpighian  body  to  the  uriniferous  ducts  and 
blood-vessels,  a,  one  of  the  interlobular  arteries;  a',  afferent  artery  passing  into  the  glomerulus;  c, 
capsule  of  the  Malpighian  body,  forming  the  termination  of  and  continuous  with  t,  the  uriniferous 
tube;  e',  e',  efferent  vessels  which  subdivide  in  the  plexus  jp,  surrounding  the  tube,  and  finally  ter- 
minate in  the  branch  of  the  renal  vein  e  (after  Bowman). 


papillary  layer,  and,  joining  with  other  collecting  tuoes,  form  larger 
tubes,  which  finally  open  at  the  apex  of  the  papilla.  These  collecting 
tubes  are  lined  with  transparent  nucleated  columnar  or  cubical  cells  (14, 
15,  16). 

The  cells  of  the  tubules  with  the  exception  of  Henle's  loop  and  all 
parts  of  the  collecting  tubules,  are,  as  a  rule,  possessed  of  the  mtra-nuclear 
as  well  as  of  the  intra-cellular  network  of  fibres,  of  which  the  vertical  rods 
are  most  conspicuous  parts. 

Heidenhain  observed  that  indigo-sulphate  of  sodium,  and  other  pig- 
ments injected  into  the  jugular  vein  of  an  animal,  were  apparently  ex- 
creted by  the  cells  which  possessed  these  rods,  and  therefore  concluded 
that  the  pigment  passes  through  the  cells,  rods,  and  nucleus  themselves. 


352  HAND-BOOK    OF    PHYSIOLOGY. 

Klein,  however,  believes  that  the  pigment  passes  through  the  intercellular 
substances,  and  not  through  the  cells. 

In  some  places,  it  is  stated  that  a  distinct  membrane  of  flattened  cells 
can  be  made  out  lining  the  lumen  of  the  tubes  (centrotubular  membrane). 

Blood-vessels  of  Kidneys. — In  connection  with  the  general  distri- 
bution of  blood-vessels  to  the  kidney,  the  Malpighian  Corpuscles  may  be 
further  considered.  They  (Fig.  243)  are  found  only  in  the  cortical  part 
of  the  kidney,  and  are  confined  to  the  central  part,  which,  however, 
makes  up  about  seven-eighths  of  the  whole  cortex.  On  a  section  of  the 
organ,  some  of  them  are  just  visible  to  the  naked  eye  as  minute  red  points; 
others  are  too  small  to  be  thus  seen.  Their  average  diameter  is  about 
T|~o  of  an  inch.  Each  of  them  is  composed,  as  we  have  seen  above,  of 
the  dilated  extremity  of  a  urinary  tube,  or  Malpighian  capsule,  enclosing 
a  tuft  of  blood-vessels. 

The  renal  artery  divides  into  several  branches,  which,  passing  in  at 
the  hilus  of  the  kidney,  and  covered  by  a  fine  sheath  of  areolar  tissue 
derived  from  the  capsule,  enter  the  substance  of  the  organ  in  the  inter- 
vals between  the  papillae,  chiefly  at  ths  junction  between  the  cortex  and 
the  boundary  layer.  The  chief  branches  then  pass  almost  horizontally, 
giving  off  smaller  branches  upward  to  the  cortex  and  downward  to  the 
medulla.  The  former  are  for  the  most  part  straight,  they  pass  almost 
vertically  to  the  surface  of  the  kidney,  giving  off  laterally  in  all  directions 
longer  or  shorter  branches,  which  supply  the  afferent  arteries  to  the  Mal- 
pighiaii  bodies. 

The  small  afferent  artery  (Figs.  243  and  245)  which  enters  the  Mal- 
pighian corpuscle,  breaks  up  as  before  mentioned  in  the  interior  into  a 
dense  and  convoluted  and  looped  capillary  plexus,  which  is  ultimately 
gathered  up  again  into  a  single  small  efferent  vessel,  comparable  to  a  min- 
ute vein,  which  leaves  the  Malpighian  capsule  just  by  the  point  at  which 
the  afferent  artery  enters  it.  On  leaving,  it  does  not  immediately  join 
other  small  veins  as  might  have  been  expected,  but  again  breaking  up  into 
a  network  of  capillary  vessels,  is  distributed  on  the  exterior  of  the  tubule, 
from  whose  dilated  end  it  had  just  emerged.  After  this  second  breaking 
up  it  is  finally  collected  into  a  small  vein,  which,  by  union  with  others 
like  it,  helps  to  form  the  radicles  of  the  renal  vein.  Thus,  in  the  kidney, 
the  blood  entering  by  the  renal  artery  traverses  two  sets  of  capillaries  be- 
fore emerging  by  the  renal  vein,  an  arrangement  which  may  be  compared 
to  the  portal  system  in  miniature. 

The  tuft  of  vessels  in  the  course  of  development  is,  as  .  were,  thrust 
into  the  dilated  extremity  of  the  urinary  tubule,  which  finally  completely 
invests  it  just  as  the  pleura  invests  the  lungs  or  the  tunica  vaginalis  the 
testicle.  Thus  the  Malpighian  capsule  is  lined  by  a  parietal  layer  of 
squamous  cells  and  a  visceral  or  reflected  layer  immediately  covering  the 
vascular  tuft  (Fig.  241),  and  sometimes  dipping  down  into  its  interstices. 


THE    KIDNEYS    AND    VRINE. 


353 


This  reflected  layer  of  epithelium  is  readily  seen  in  young  subjects,  but 
cannot  always  be  demonstrated  in  the  adult.  (See  Figs.  244  and  245.) 

The  vessels  \viiich  enter  the  medullary  layer  break  up  into  smaller 
arterioles,  which  pass  through  the  boundary  layer  and  proceed  in  a 
straight  course  between  the  tubules  of  the  papillary  layer,  giving  off  on 
their  way  branches,  which  form  a  fine  arterial  meshwork  around  the  tubes, 
and  end  in  a  similar  plexus,  from  which  the  venous  radicles  arise. 

Besides  the  small  afferent  arteries  of  the  Malpighian  bodies,  there  are, 
of  course,  others  which  are  distributed  in  the  ordinary  manner,  for  nutri- 
tion's sake,  to  the  different  parts  of  the  organ;  and  in  the  pyramids,  be- 


FIG.  244. 


FIG.  245. 


lie  and  tuft,  with  the  commencement  of  a 


FIG.  244.— Transverse  section  of  a  developing  Malpighian  capsule  and  tuft  (human)  x  300.  From 
a  foetus  at  about  the  fourth  month;  a,  flattened  cells  growing  to  form  the  capsule;  6,  more  rounded 
cells,  continuous  with  the  above,  reflected  round  c,  and  finally  enveloping  it;  c,  mass  of  embryonic 
cells  which  will  later  become  developed  into  blood-vessels.  (W.  Pye.) 

FIG.  245. — Epithelial  elements  or  a  Malpighian  ca; 
urinary  tubule  showing  the  afferent  and  efferent 
capsule ;  b,  similar,  but  rather  lar 
the  vessels  of  the  capillary  tuft 
of  it.    (W.  Pye.) 

tween  the  tubes,  there  are  numerous  straight  vessels,  the  vasta  recta,  sup- 
posed by  some  observers  to  be  branches  of  vasa  efferentia  from  Malpighian 
bodies,  and  therefore  comparable  to  the  venous  plexus  around  the  tubules 
in  the  cortical  portion,  while  others  think  that  they  arise  directly  from 
small  branches  of  the  renal  arteries. 

Between  the  tubes,  vessels,  etc.,  which  make  up  the  substance  of  the 
kidney,  there  exists,  in  small  quantity,  a  fine  matrix  of  areolar  tissue. 

Nerves. — The  nerves  of  the  kidney  are  derived  from  the  renal  plexus. 

Structure  of  the  Ureters. — The  duct  of  the  kidney,  or  ureter,  is  a 

tube  about  the  size  of  a  goose-quill,  and  from  a  foot  to  sixteen  inches  in 

length,   which,   continuous  above  with  the  pelvis  of  the  kidney,  ends 

below  by  perforating  obliquely  the  walls  of  the  bladder,  and  opening  on 

VOL.  I.— 23. 


354  HAND-BOOK    OF    PHYSIOLOGY. 

its  internal  surface.  It  is  constructed  of  three  principal  coats  (a)  an 
outer,  tough,  fibrous  and  elastic  coat;  (b)  a  middle,  muscular  coat,  of 
which  the  fibres  are  unstriped,  and  arranged  in  three  layers — the  fibres 
of  the  central  layer  being  circular,  and  those  of  the  other  two  longitudinal 
in  direction;  and  (c)  an  internal  mucous  lining  continuous  with  that  of 
the  pelvis  of  the  kidney  above,  and  of  the  urinary  bladder  below.  The 
epithelium  of  all  these  parts  (Fig.  246)  is  alike  stratified  and  of  a  some- 
what peculiar  form;  the  cells  on  the  free  surface  of  the  mucous  mem- 
brane being  usually  spheroidal  or  polyhedral  with  one  or  more  spherical  or 
oval  nuclei;  while  beneath  these  are  pear-shaped  cells,  of  which  the  broad 
ends  are  directed  toward  the  free  surface,  fitting  in  beneath  the  cells  of 
the  first  row,  and  the  apices  are  prolonged  into  processes  of  various 
lengths,  among  which,  again,  the  deepest  cells  of  the  epithelium  are 
found  spheroidal,  irregularly  oval,  spindle-shaped  or  conical. 

Structure  of  Urinary  Bladder. — The  urinary  bladder,  which 
forms  a  receptacle  for  the  temporary  lodgment  of  the  urine  in  the  intervals 
of  its  expulsion  from  the  body,  is  more  or  less  pyriform,  its  widest  part, 
which  is  situate  above  and  behind,  being  termed  the  fundus:  and  the 
narrow  constricted  portion  in  front  and  below,  by  which  it  becomes  con- 
tinuous with  the  urethra,  being  called  its  cervix  or  neck.  It  is  constructed 
of  four  principal  coats, — serous,  muscular,  areolar  or  submucous,  and 
mucous,  (a)  The  serous  coat,  which  covers  only  the  posterior  and  upper 
half  of  the  bladder,  has  the  same  structure  as  that  of  the  peritoneum. 


FIG.  246.— Epithelium  of  the  bladder;  a,  one  of  the  cells  of  the  first  row;  6,  a  cell  of  the  second 
row;  c,  cells  in  situ,  of  first,  second,  and  deepest  layers.    (Obersteiner.) 

with  which  it  is  continuous,  (b)  The  fibres  of  the  muscular  coat,  which 
are  unstriped,  are  arranged  in  three  principal  layers,  of  which  the  external 
and  internal  (Ellis)  have  a  general  longitudinal,  and  the  middle  layer  a 
circular  direction.  The  latter  are  especially  developed  around  the  cervix 
of  the  organ,  and  are  described  as  forming  a  sphincter  vesicce.  The  mus- 
cular fibres  of  the  bladder,  like  those  of  the  stomach,  are  arranged  not  in 
simple  circles,  but  in  figure-of-8  loops,  (c)  The  areolar  or  submucous 
coat  is  constructed  of  connective  tissue  with  a  large  proportion  of  elastic 
fibres,  (d)  The  mucous  membrane,  which  is  rugose  in  the  contracted 
state  of  the  organ,  does  not  differ  in  essential  structure  from  mucous 


THE    KIDNEYS    AND    URINE.  355 

membranes  in  general.  Its  epithelium  is  stratified  and  closely  resembles 
that  of  the  pelvis  of  the  kidney  and  the  ureter  (Fig.  240). 

The  mucous  membrane  is  provided  with  mucous  glands,  which  are 
more  numerous  near  the  neck  of  the  bladder. 

The  bladder  is  well  provided  with  blood  and  lymph  vessels,  and  with 
nerves.  The  latter  are  branches  from  the  sacral  plexus  (spinal)  and  hypo- 
gastric  plexus  (sympathetic).  A  few  ganglion-cells  are  found,  here  and 
there,  in  the  course  of  the  nerve-fibres. 

THE  EXCRETION  OF  THE  KIDNEY  : — THE  URINE. 

Physical  Properties. — Healthy  urine  is  a  perfectly  transparent, 
amber-colored  liquid,  with  a  peculiar,  but  not  disagreeable  odor,  a  bitter- 
ish taste,  and  slight  acid  reaction.  Its  specific  gravity  varies  from  1015 
to  1025.  On  standing  for  a  short  time,  a  little  mucous  appears  in  it  as 
a  flocculent  cloud. 

Chemical  Composition. — The  urine  consists  of  water,  holding  in 
solution  certain  organic  and  saline  matters  as  its  ordinary  constituents, 
and  occasionally  various  matters  taken  into  the  stomach  as  food — salts, 
coloring  matter,  and  the  like.  * 

Table  of  the  Chemical  Composition  of  the  Urine  (modified  from  Becquer el). 

Water  .  967 

Urea 14.230 

Other  nitrogenous  crystalline  bodies — 

Uric  acid,  principally  in  the  form  of  alkaline 
urates,  a  trace  only  free. 


Kreatinin,  xanthin,  hypoxanthin. 

Hippuric  acid,  leucin,  tyrosin,  taurin,  cys- 
tin,  etc.,  all  in  small  amounts  and  not 
constant. 

Mucus  and  pigment. 
Salts  :— 

Inorganic — 

Principally  sulphates,  phosphates,  and  chlo- 
rides of  sodium,  and  potassium,  with  phos- 
phates of  magnesium  and  calcium,  traces 


10-635 


8-135 


of  silicates  and  of  chlorides. 
Organic — 

Lactates,  hippurates,  acetates  and  formates, 
which  only  appear  occasionally. 

Sugar         .  a  trace  sometimes. 

Gases  (nitrogen  and  carbonic  acid  principally). 

1000 

Reaction   of  the    Urine — The  normal  reaction    of  the  urine  is 
slightly  acid.     This  acidity  is  due  to  acid  phosphate  of  sodium,  and  is 


356  HAND-BOOK    OF    PHYSIOLOGY. 

less  marked  after  meals.  The  urine  contains  no  appreciable  amount  uof 
free  acid,  as  it  gives  no  precipitate  with  sodium  hyposulphite.  After 
standing  for  some  time  the  acidity  increases  from  a  kind  of  fermentation, 
due  in  all  probability  to  the  presence  of  mucus,  and  acid  urates  or  free 
uric  acid  is  deposited.  After  a  time,  varying  in  length  according  to  the 
temperature,  the  reaction  becomes  strongly  alkaline  from  the  change  of 
urea  into  ammonium  carbonate — while  at  the  same  time  a  strong  ammoni- 
acal  and  foetid  odor  appears,  with  deposits  of  triple  phosphates  and  alka- 
line urates.  As  this  does  not  occur  unless  the  urine  is  exposed  to  the 
air,  or,  at  least,  until  air  has  had  access  to  it,  it  is  probable  that  the  de- 
composition is  due  to  atmospheric  germs. 

Reaction  of  Urine  in  different  classes  of  Animals. — In  most  herbivo- 
rous animals  the  urine  is  alkaline  and  turbid.  The  difference  depends, 
not  on  any  peculiarity  in  the  mode  of  secretion,  but  on  the  differences  in 
the  food  on  which  the  two  classes  subsist:  for  when  carnivorous  animals, 
such  as  dogs,  are  restricted  to  a  vegetable  diet,  their  urine  becomes  pale, 
turbid,  and  alkaline,  like  that  of  an  herbivorous  animal,  but  resumes  its 
former  acidity  on  the  return  to  an  animal  diet;  while  the  urine  voided  by 
herbivorous  animals,  e.g.,  rabbits,  fed  for  some  time  exclusively  upon 
animal  substances,  presents  the  acid  reaction  and  other  qualities  of  the 
urine  of  Carnivora,  its  ordinary  alkalinity  being  restored  only  on  the 
substitution  of  a  vegetable  for  the  animal  diet.  Human  urine  is  not 
usually  rendered  alkaline  by  vegetable  diet,  but  it  becomes  so  after  the 
free  use  of  alkaline  medicines,  or  of  the  alkaline  salts  with  carbonic  or 
vegetable  acids;  for  these  latter  are  changed  into  alkaline  carbonates  pre- 
vious to  elimination  by  the  kidneys. 

AVERAGE    QUANTITY    OF    THE   CHIEF   CONSTITUENTS   OF  THE   URINE 
EXCRETED  IN  24  HOURS  BY  HEALTHY  MALE  ADULTS  (PARKES). 

• 

Water 52-     fluid  ounces. 

Urea 512 '4  grains. 

Uric  acid  ....  8-5 

Hippuric  acid,  uncertain          probably  10  to  15*         " 

Sulphuric  acid 31-11      " 

Phosphoric  acid 45*         " 

Potassium,  Sodium,  Ammonium  Chlorides  )  323-25      " 
and  free  Chlorine  .         .         .         .  j 

Lime 3'5 

Magnesia 3* 

Mucus 7*         " 

{Kreatinin 
Sffin  }•  .         .     154- 

Hypoxanthin 
Eesinous  matter,  etc. 

Variations  in  Quantity  of  Constituents.— From  these  proportions, 
however,  most  of  the  constituents  are,  even  in  health,  liable  to  variations. 


THE    KIDNEYS    AND    URINE.  357 

The  variations  of  the  water  in  different  seasons,  and  according  to  the 
quantity  of  drink  and  exercise,  have  already  been  mentioned.  The  water 
of  the  urine  is  also  liable  to  be  influenced  by  the  condition  of  the  nervous 
system,  being  sometimes  greatly  increased  in  hysteria,  and  some  other 
nervous  affections;  and  at  other  times  diminished.  In  some  diseases  it  is 
enormously  increased;  and  its  increase  may  be  either  attended  with  an  aug- 
mented quantity  of  solid  matter,  as  in  ordinary  diabetes,  or  may  be  nearly 
the  sole  change,  as  in  the  affection  termed  diabetes  insipidus.  In  other 
diseases,  e.g. .  the  various  forms  of  albuminuria,  the  quantity  may  be  con- 
siderably diminished.  A  febrile  condition  almost  always  diminishes  the 
quantity  of  water;  and  a  like  diminution  is  caused  by  any  affection  which 
draws  off  a  large  quantity  of  fluid  from  the  body  through  any  other  chan- 
nel than  that  of  the  kidneys,  e.g.,  the  bowels  or  the  skin. 

Method  of  estimating  the  Solids. — A  useful  rule  for  approximately 
estimating  the  total  solids  in  any  given  specimen  of  healthy  urine  is  to 
multiply  the  last  two  figures  representing  the  specific  gravity  by  2*33. 
Thus,  in  urine  of  sp.  gr.  1025,  2 '33x25 =58 '25  grains  of  solids,  are  con- 
tained in  1000  grains  of  the  urine.  In  using  this  method  it  must  be 
remembered  that  the  limits  of  error  are  much  wider  in  diseased  than  in 
healthy  urine. 

Variations  in  the  Specific  Gravity. — The  specific  gravity  of  the 
human  urine  is  about  1020.  Probably  no  other  animal  fluid  presents  so 
many  varieties  in  density  within  twenty-four  hours  as  the  urine  does;  for 
the  relative  quantity  of  water  and  of  solid  constituents  of  which  it  is 
composed  is  materially  influenced  by  the  condition  and  occupation  of  the 
body  during  the  time  at  which  it  is  secreted,  by  the  length  of  time  which 
has  elapsed  since  the  last  meal,  and  by  several  other  accidental  circum- 
stances. The  existence  of  these  causes  of  difference  in  the  composition 
of  the  urine  has  led  to  the  secretion  being  described  under  the  three  heads 
of  urina  sanguinis,  urina  potus,  and  urina  cibi.  The  first  of  these 
names  signifies  the  urine,  or  that  part  of  it  which  is  secreted  from 
the  blood  at  times  in  which  neither  food  nor  drink  has  been  recently 
taken,  and  is  applied  especially  to  the  urine  which  is  evacuated  in  the 
morning  before  breakfast.  The  term  urina  potus  indicates  the  urine 
secreted  shortly  after  the  introduction  of  any  considerable  quantity  of 
fluid  into  the  body:  and  the  urina  cibi,  the  portions  secreted  during  the 
period  immediately  succeeding  a  meal  of  solid  food.  The  last  kind  con- 
tains a  larger  quantity  of  solid  matter  than  either  of  the  others;  the  first 
or  second,  being  largely  diluted  with  water,  possesses  a  comparatively 
low  specific  gravity.  Of  these  three  kinds,  the  morning  urine  is  the  best 
calculated  for  analysis  in  health,  since  it  represents  the  simple  secretion 
unmixed  with  the  elements  of  food  or  drink;  if  it  be  not  used,  the  whole 
of  the  urine  passed  during  a  period  of  twenty-four  hours  should  be  taken. 


358  HAND-BOOK    OF    PHYSIOLOGY. 

In  accordance  with  the  various  circumstances  above-mentioned,  the 
specific  gravity  of  the  urine  may,  consistently  with  health,  range  widely 
on  both  sides  of  the  usual  average.  The  average  healthy  range  may  be 
stated  at  from  1015  in  the  winter  to  1025  in  the  summer;  but  variations 
of  diet  and  exercise,  and  many  other  circumstances,  may  make  even  greater 
differences  than  these.  In  disease,  the  variation  may  be  greater;  some- 
times descending,  in  albuminuria,  to  1004,  and  frequently  ascending  in 
diabetes,  when  the  urine  is  loaded  with  sugar,  to  1050,  or  even  to  1060. 

Quantity. — The  total  quantity  of  urine  passed  in  twenty-four  hours 
is  affected  by  numerous  circumstances.  On  taking  the  mean  of  many 
observations  by  several  experimenters,  the  average  quantity  voided  in 
twenty-four  hours  by  healthy  male  adults  from  20  to  40  years  of  age  has 
been  found  to  amount  to  about  52 -J-  fluid  ounces  (1-J-  to  2  litres). 

Abnormal  Constituents. — In  disease,  or  after  the  ingestion  of 
special  foods,  various  abnormal  substances  occur  in  urine,  of  which  the 
following  may  be  mentioned — serum-albumin,  globulin,  ferments  (ap- 
parently present  in  health  also),  blood,  sugar,  bile  acids,  and  pigments, 
fats,  oxalates,  various  salts  taken  as  medicine,  and  other  matters,  as  bac- 
teria and  renal  casts. 

THE  SOLIDS  OF  THE  UKINE. 

Urea  (CH4N20). — Urea  is  the  principal  solid  constituent  of  the 
urine,  forming  nearly  one-half  of  the  whole  quantity  of  solid  matter.  It 
is  also  the  most  important  ingredient,  since  it  is  the  chief  substance  by 
which  the  nitrogen  of  decomposed  tissue  and  superfluous  food  is  excreted 

from  the  body.  For  its  removal,  the  secre- 
tion of  urine  seems  especially  provided;  and 
by  its  retention  in  the  blood  the  most  per- 
nicious effects  are  produced. 

Properties. — Urea,  like  the  other  solid 
constituents  of  the  urine,  exists  in  a  state 
of  solution.  But  it  may  be  procured  in  the 
solid  state,  and  then  appears  in  the  form  of 
delicate  silvery  acicular  crystals,  which, 
under  the  microscope,  appear  as  four-sided 
prisms  (Fig.  247).  It  is  obtained  in  this 
FIG.  247.-Crystaisof  urea.  state  bJ  evaporating  urine  carefully  to  the 

consistence  of  honey,  acting  on  the  inspis- 
sated mass  with  four  parts  of  alcohol,  then  evaporating  the  alcoholic 
solution,  and  purifying  the  residue  by  repeated  solution  in  water  or  alco- 
hol, and  finally  allowing  it  to  crystallize.  It  readily  combines  with 
some  acids,  like  a  weak  base;  and  may  thus  be  conveniently  procured 
in  the  form  of  crystals  of  nitrate  or  oxalate  of  urea. 


THE    KIDNEYS    AND    URIXE.  359 

U.ea  is  colorless  when  pure;  when  impure,  yellow  or  brown:  without 
smell,  and  of  a  cooling  nitre-like  taste;  has  neither  an  acid  nor  an  alka- 
line reaction,  and  deliquesces  in  a  moist  and  warm  atmosphere.  At  59°  F. 
(15°  C.)  it  requires  for  its  solution  less  than  its  weight  of  water;  it  is 
dissolved  in  all  proportions  by  boiling  water;  but  it  requires  five  times  its 
weight  of  cold  alcohol  for  its  solution.  It  is  insoluble  in  ether.  At  248°  F. 
(120°  C.)  it  melts  without  undergoing  decomposition;  at  a  still  higher 
temperature  ebullition  takes  place,  and  carbonate  of  ammonium  sublimes; 
the  melting  mass  gradually  acquires  a  pulpy  consistence;  and  if  the  heat 
is  carefully  regulated,  leaves  a  grey-white  powder,  cyanic  acid. 

Chemical  Nature  of  Urea. — The  chemical  nature  of  urea  is  ex- 
plained elsewhere,1  but  it  will  be  as  well  to  mention  here  that  urea  is 
isomeric  with  ammonium  cyanate,  and  that  it  was  first  artificially  pro- 
duced from  this  substance.  Thus: — Ammonium  cyanate  (NH4.CNO) 
=  urea  (CH4~N"20).  The  action  of  heat  upon  urea  in  evolving  ammonium 
carbonate  and  leaving  cyanic  acid,  is  thus  explained.  A  similar  de- 
composition of  the  urea  with  development  of  ammonium  carbonate 
ensues  spontaneously  when  urine  is  kept  for  some  days  after  being  voided, 
and  explains  the  ammoniacal  odor  then  evolved  (p.  356).  The  urea  is  some- 
times decomposed  before  it  leaves  the  bladder,  when  the  mucous  mem- 
brane is  diseased,  and  the  mucus  secreted  by  it  is  both  more  abundant, 
and,  probably,  more  prone  to  act  as  a  ferment;  although  the  decomposi- 
tion does  not  often  occur  unless  atmospheric  germs  have  had  access  to 
the  urine. 

Variations  in  the  Quantity  of  Urea. — The  quantity  of  urea  ex- 
creted is,  like  that  of  the  urine  itself,  subject  to  considerable  variation. 
For  a  healthy  adult  500  grains  (about  32 -5  grms.)  per  diem  maybe  taken 
as  rather  a  high  average.  Its  percentage  in  healthy  urine  is  1  *5  to  2  '5. 
It  is  materially  influenced  by  diet,  being  greater  when  animal  food  is  ex- 
clusively used,  less  when  the  diet  is  mixed,  and  least  of  all  with  a  vegeta- 
ble diet.  As  a  rule,  men  excrete  a  larger  quantity  than  women,  and  per- 
sons in  the  middle  periods  of  life  a  larger  quantity  than  infants  or  old 
people.  The  quantity  of  urea  excreted  by  children,  relatively  to  their 
body-weight,  is  much  greater  than  in  adults.  Thus  the  quantity  of  urea 
excreted  per  kilogram  of  weight  was,  in  a  child,  0'8  grm. :  in  an  adult 
only  0*4  grm.  Regarded  in  this  way,  the  excretion  of  carbonic  acid 
gives  similar  result,  the  proportion  in  the  child  and  adult  being  as  82  : 34. 

The  quantity  of  urea  does  not  necessarily  increase  and  decrease  with 
that  of  the  urine,  though  on  the  whole  it  would  seem  that  whenever  the 
amount  of  urine  is  much  augmented,  the  quantity  of  urea  also  is  usually 
increased;  and  it  appears  that  the  quantity  of  urea,  as  of  urine,  may  be 
especially  increased  by  drinking  large  quantities  of  water.  In  various 

1  Appendix. 


360  HAND-BOOK    OF    PHYSIOLOGY. 

diseases  the  quantity  is  reduced  considerably  below  the  healthy  standard, 
while  in  other  affections  it  is  above  it. 

Estimation  of  Urea. — A  convenient  apparatus  for  estimating  the 
quantity  of  urea  in  a  given  sample  of  urine  is  that  devised  by  Russell  and 
West. 

Urea  contains  nearly  half  its  weight  of  nitrogen;  hence  this  gas  may 
be  taken  as  a  measure  of  the  urea.  A  small  quantity  of  urine  is  mixed 
with  a  large  excess  of  solution  of  sodium  hypobromite,  which  completely 
decomposes  the  urea,  liberating  all  the  nitrogen  in  a  gaseous  form:  a 
gentle  heat  promotes  the  reaction.  The  percentage  of  urea  can  of  course 
be  readily  calculated  from  the  volume  of  nitrogen  evolved  from  a  measured 
quantity  of  the  urine,  but  this  calculation  is  avoided  by  graduating  the 
tube  in  which  the  nitrogen  is  collected  with  numbers  which  indicate  the 
corresponding  percentage  of  urea.  CON2H4  -j-  3NaBrO  -f-  2NaHO  = 
3NaBr  +  3H20  +  Na2C03  +  N9. 

Uric  Acid  (C5H4N403). — This  substance,  which  was  formerly  termed 
lithic  acid,  on  account  of  its  existence  in  many  forms  of  urinary  calculi, 
is  rarely  absent  from  the  urine  of  man  or  animals,  though  in  the  feline 
tribe  it  seems  to  be  sometimes  entirely  replaced  by  urea.  The  pro- 
portionate quantity  of  uric  acid  varies  considerably  in  different  animals. 
In  man,  and  Mammalia  generally,  especially  the  Herbivora,  it  is  com- 
paratively small.  .  In  the  whole  tribe  of  birds,  and  of  serpents,  on  the 
other  hand,  the  quantity  is  very  large,  greatly  exceeding  that  of  the  urea. 
In  the  urine  of  granivorous  birds,  indeed,  urea  is  rarely  if  ever  found,  its 
place  being  entirely  supplied  by  uric  acid. 

Variations  in  Quantity.— The  quantity  of  uric  acid,  like  that  of 
urea,  in  human  urine,  is  increased  by  the  use  of  animal  food,  and  de- 
creased by  the  use  of  food  free  from  nitrogen,  or  by  an  exclusively  vege- 
table diet.  In  most  febrile  diseases,  and  in  plethora,  it  is  formed  in  un- 
naturally large  quantities;  and  in  gout  it  is  deposited  in,  and  around, 
joints,  in  the  form  of  urate  of  soda,  of  which  the  so-called  chalk-stones 
of  this  disease  are  principally  composed.  The  average  amount  secreted 
in  twenty -four  hours  is  8*5  grains  (rather  more  than  half  a  gramme). 

Condition  of  Uric  Acid  in  the  Urine. — The  condition  in  which 
uric  acid  exists  in  solution  in  the  urine  has  formed  ths  subject  of  some 
discussion,  because  of  its  difficult  solubility  in  water.  It  is  found  chiefly 
in  the  form  of  urate  of  sodium,  produced  by  the  uric  acid  as  soon  as  it  is 
formed,  combining  with  part  of  the  base  of  the  alkaline  sodium  phosphate 
of  the  blood.  Hippuric  acid,  which  exists  in  human  urine  also,  acts  upon 
the  alkaline  phosphate  in  the  same  way,  and  increases  still  more  the  quan- 
tity of  acid  phosphate,  on  the  presence  of  which  it  is  probable  that  a  part 
of  the  natural  acidity  of  the  urine  depends.  It  is  scarcely  possible  to  say 
whether  the  union  of  uric  acid  with  the  base  sodium  and  probably  ammo- 
nium, takes  place  in  the  blood,  or  in  the  act  of  secretion  in  the  kidney: 


THE    KIDNEYS    AND    URINE. 


361 


the  latter  is  the  more  likely  opinion;  but  the  quantity  of  either  uric  acid 
or  urates  in  the  blood  is  probably  too  small  to  allow  of  this  question  being 
solved. 

Owing  to  its  existence  in  combination  in  healthy  urine,  uric  acid  for 
examination  must  generally  be  precipitated  from  its  bases  by  a  stronger 
acid.  Frequently,  however,  when  excreted  in  excess,  it  is  deposited  in  a 
crystalline  form  (Fig.  248),  mixed  with  large  quantities  of  ammonium  or 
sodium  urate.  In  such  cases  it  may  be  procured  for  microscopic  exami- 
nation by  gently  warming  the  portion  of  urine  containing  the  sediment; 
this  dissolves  urate  of  ammonium  and  sodium,  while  the  comparatively 
insoluble  crystals  of  uric  acid  subside  to  the  bottom. 

The  most  common  form  in  which  uric  acid  is  deposited  in  urine,  is  that 
of  a  brownish  or  yellowish  powdery  substance,  consisting  of  granules  of 


FIG.  248.— Various  forms  of  uric  acid  crystals. 


FIG.  349.— Crystals  of  hippuric  acid. 


ammonium — or  sodium  urate.  "When  deposited  in  crystals,  it  is  most 
frequently  in  rhombic  or  diamond-shaped  laminae,  but  other  forms  are  not 
uncommon  (Fig.  248).  When  deposited  from  the  urine,  the  crystals  are 
generally  more  or  less  deeply  colored,  from  being  combined  with  the 
coloring  principles  of  the  urine. 

There  are  two  chief  tests  for  uric  acid  besides  the  microscopic  evidence 
of  its  crystalline  structure:  (1)  The  Murexide  test,  which  consists  of 
evaporating  to  dryness  a  mixture  of  strong  nitric  acid  and  uric  acid  in  a 
water  bath.  This  leaves  a  yellowish-red  residue  of  Alloxan  (C4H2N204) 
and  urea,  and  -this,  on  addition  of  ammonium  hydrate,  gives  a  beautiful 
purple  (ammonium  purpurate,  C8H4  (NH4)  Nfi06),  deepened  on  addition 
of  caustic  potash.  (2)  Schiff's  test.  Dissolve  the  uric  acid  in  sodium 
carbonate  solution,  and  drop  some  of  it  on  a  filter  paper  moistened  with 
silver  nitrate,  a  black  spot  appears,  which  corresponds  to  the  reduction 
of  silver  by  the  uric  acid. 

Hippuric  Acid  (C9H9N03)  has  long  been  known  to  exist  in  the  urine 
of  herbivorous  animals  in  combination  with  soda.  It  also  exists  naturally 


362  HAND-BOOK    OF    PHYSIOLOGY. 

in  the  urine  of  man,  in  quantity  equal  or  rather  exceeding  that  of  the 
uric  acid. 

Pigments. — The  coloring  matters  of  the  urine  are:  (1)  Uro-MUn, 
a  substance  connected  with  the  coloring  matters  of  the  blood  and  bile 
(p.  275);  it  is  especially  seen  in  febrile  urine  and  exists  normally,  but 
to  less  amount;  it  is  of  a  yellowish-red  color;  (2)  Uro-clirome,  which  on 
exposure  undergoes  oxidation,  and  becomes  Uro-erythrin,  the  former 
being  yellowish  and  the  latter  sandy  red;  and  (3)  Indican  is  occasionally 
present. 

Indican  is  not  itself  pigmentary,  though  by  its  decomposition  indigo 
blue  and  indigo  red  are  produced.  Its  presence  can  usually  be  detected 
by  adding  to  a  small  quantity  of  urine  an  equal  bulk  of  strong  hydrochloric 
acid,  and  gently  heating  the  solution;  on  the  addition  of  two  or  three 
drops  of  strong  nitric  acid  a  delicate  purplish  tint  is  developed,  and  indigo 
blue  and  red  crystals  separate  out. 

Mucus. — Mucus  in  the  urine  consists  principally  of  the  epithelial 
debris  of  the  mucous  surface  of  the  urinary  passages.  Particles  of  epithe- 
lium, in  greater  or  less  abundance,  may  be  detected  in  most  samples  of 
urine,  especially  if  it  has  remained  at  rest  for  some  time  and  the  lower 
strata  are  then  examined  (Fig.  250).  As  urine  cools,  the  mucous  is  some- 


FIG.  250.— Mucus  deposited  from  urine. 

times  seen  suspended  in  it  as  a  delicate  opaque  cloud,  but  generally  it 
falls.  In  inflammatory  affections  of  the  urinary  passages,  especially  of 
the  bladder,  mucus  in  large  quantities  is  poured  .forth,  and  speedily  un- 
dergoes decomposition.  The  presence  of  the  decomposing  mucus  excites 
(as  already  stated,  p.  356)  chemical  changes  in  the  urea,  whereby  ammo- 
nia, or  carbonate  of  ammonium,  is  formed,  which,  combining  with  the 
excess  of  acid  in  the  super-phosphates  in  the  urine,  produces  insoluble 
neutral  or  alkaline  phosphates  of  calcium  and  magnesium,  and  phosphate 
of  ammonium  and  magnesium.  These  mixing  with  the  mucus,  constitute 
the  peculiar  white,  viscid,  mortar-like  substance  which  collects  upon  the 
mucous  surface  of  the  bladder,  and  is  often  passed  with  the  urine,  form- 
ing a  thick  tenacious  sediment. 


THE    KIDNEYS    AND    URINE.  363 

Extractives. — Besides  mucus  and  coloring  matter,  urine  contains  a 
considerable  quantity  of  nitrogenous  compounds,  usually  described  under 
the  generic  name  of  extractives.  Of  these,  the  chief  are:  (1)  Kreatinin. 
(C4H7N3O)  a  substance  derived,  probably,  from  the  metamorphosis  of  mus- 
cular tissue,  crystallizing  in  colorless  oblique  rhombic  prisms;  a  fairly 
definite  amount  of  this  substance,  about  15  grains  (1  grm.),  appears  in 
the  urine  daily,  so  that  it  must  be  looked  upon  as  a  normal  constituent;  it 
is  increased  on  an  increase  of  the  nitrogenous  constituents  of  the  food; 
(2)  Xanthin  (C6N4H402),  an  amorphous  powder  soluble  in  hot  water;  (3) 
Hypo-zanthin,  or  sarkin  (CBN4H40);  (4)  Oxaluric  acid  (C3H4N204),  in 
combination  with  ammonium;  (5)  Allantoin  (C4H6N203),  in  the  urine 
of  the  new-born  child.  All  these  extractives  are  chiefly  interesting  as 
being  closely  connected  with  urea,  and  mostly  yielding  that  substance  on 
oxidation.  Leucin  and  tyrosin  can  scarcely  be  looked  upon  as  normal 
constituents  of  urine. 

Saline  Matter. — The  sulphuric  acid  in  the  urine  is  combined  chiefly 
or  entirely  with  sodium  or  potassium;  forming  salts  which  are  taken  in 
very  small  quantity  with  the  food,  and  are  scarcely  found  in  other  fluids 
or  tissues  of  the  body;  for  the  sulphates  commonly  enumerated  among 
the  constituents  of  the  ashes  of  the  tissues  and  fluids  are  for  the  most 
part,  or  entirely,  produced  by  the  changes  that  take  place  in  the  burn- 
ing. Only  about  one-third  of  the  sulphuric  acid  found  in  the  urine  is 
derived  directly  from  the  food  (Parkes).  Hence  the  greater  part  of  the 
sulphuric  acid  which  the  sulphates  in  the  urine  contain,  must  be  formed 
in  the  blood,  or  in  the  act  of  secretion  of  urine;  the  sulphur  of  which  the 
acid  is  formed  being  probably  derived  from  the  decomposing  nitrogenous 
tissues,  the  other  elements  of  which  are  resolved  into  urea  and  uric  acid. 
It  may  be  in  part  derived  also  from  the  sulphur-holding  taurin  and 
cystin,  which  can  be  found  in  the  liver,  lungs,  and  other  parts  of  the 
body,  but  not  generally  in  the  excretions;  and  which,  therefore,  must  be 
broken  up.  The  oxygen  is  supplied  through  the  lungs,  and  the  heat  gen- 
erated during  combination  with  the  sulphur,  is  one  of  the  subordinate 
means  by  which  the  animal  temperature  is  maintained. 

Besides  the  sulphur  in  these  salts,  some  also  appears  to  be  in  the  urine, 
uncombined  with  oxygen;  for  after  all  the  sulphates  have  been  re- 
moved from  urine,  sulphuric  acid  may  be  formed  by  drying  and  burning 
it  with  nitre.  From  three  to  five  grains  of  sulphur  are  thus  daily  ex- 
creted. The  combination  in  which  it  exists  is  uncertain:  possibly  it  is  in 
some  compound  analogous  to  cystin  or  cystic  oxide  (p.  365).  Sulphuric 
acid  also  exists  normally  in  the  urine  in  combination  with  phenol 
(C6H6O)  as  phenol  sulphuric  acid  or  its  corresponding  salts,  with 
sodium,  etc. 

The  phosphoric  acid  in  the  urine  is  combined  partly  with  the  alkalies, 
partly  with  the  alkaline  earths — about  four  or  five  times  as  much  with 


364  HAND-BOOK    OF    PHYSIOLOGY. 

the  former  as  with  the  latter.  In  blood,  saliva,  and  other  alkaline  fluids 
of  the  body,  phosphates  exist  in  the  form  of  alkaline,  neutral,  or  acid 
salts.  In  the  urine  they  are  acid  salts,  viz.,  the  sodium,  ammonium, 
calcium,  and  magnesium  phosphates,  the  excess  of  acid  being  (Liebig) 
due  to  the  appropriation  of  the  alkali  with  which  the  phosphoric  acid  in 
the  blood  is  combined,  by  the  several  new  acids  which  are  formed  or  dis- 
charged at  the  kidneys,  namely,  the  uric,  hippuric,  and  sulphuric  acids, 
all  of  which  are  neutralized  with  soda. 

The  phosphates  are  taken  largely  in  both  vegetable  and  animal  food; 
some  thus  taken  are  excreted  at  once;  others,  after  being  transformed 
and  incorporated  with  the  tissues.  Calcium  phosphate  forms  the  prin- 
cipal earthy  constituent  of  bone,  and  from  the  decomposition  of  the  osse- 
ous tissue  the  urine  derives  a  large  quantity  of  this  salt.  The  decompo- 
sition of  other  tissues  also,  but  especially  of  the  brain  and  nerve-sub- 
stance, furnishes  large  supplies  of  phosphorus  to  the  urine,  which 


FIG.  251. — Urinary  sediment  of  triple  phosphates  (large  prismatic  crystals)  and  urate  of  am- 
monium, from  urine  which  had  undergone  alkaline  fermentation. 

phosphorus  is  supposed,  like  the  sulphur,  to  be  united  with  oxygen,  and 
then  combined  with  bases.  This  quantity  is,  however,  liable  to  consid- 
erable variation.  Any  undue  exercise  of  the  brain,  and  all  circumstances 
producing  nervous  exhaustion,  increase  it.  The  earthy  phosphates  are 
more  abundant  after  meals,  whether  on  animal  or  vegetable  food,  and  are 
diminished  after  long  fasting.  The  alkaline  phosphates  are  increased 
after  animal  food,  diminished  after  vegetable  food.  Exercise  increases 
the  alkaline,  but  not  the  earthy  phosphates  (Bence  Jones).  Phosphorus 
uncombined  with  oxygen  appears,  like  sulphur,  to  be  excreted  in  the 
urine  (Ronalds).  When  the  urine  undergoes  alkaline  fermentation, 
phosphates  are  deposited  in  the  form  of  a  urinary  sediment,  consisting 
chiefly  of  ammonio-magnesium  phosphate  (triple  phosphate)  (Fig.  251). 
This  compound  does  not,  as  such,  exist  in  healthy  urine.  The  ammonia 
is  chiefly  or  wholly  derived  from  the  decomposition  of  urea  (p.  359). 

The  chlorine  of  the  urine  occurs  chiefly  in  combination  with  sodium, 
but  slightly  also  with  ammonium,  and  perhaps  potassium.     As  the  chlo- 


THE    KIDNEYS    AND    URINE. 


365 


rides  exist  largely  in  food  and  in  most  of  the  animal  fluids,  their  occur- 
rence in  the  urine  is  easily  understood. 

Cystin  (C3H,NSOa)  (Fig.  252)  is  an  occasional  constituent  of  urine. 
It  resembles  tauriu  in  containing  a  large  quantity  of  sulphur — more  than 
25  per  cent.  It  does  not  exist  in  healthy  urine. 

Another  common  morbid  constituent  of  the  urine  is  oxalic  acid,  whicli 
is  frequently  deposited  in  combination  with  calcium  (Fig.  253)  as  a 


FIG.  252.— Crystals  of  cystin. 


FIG.  253.— Crystals  of  calcium  oxalate. 


urinary  sediment.  Like  cystin,  but  much  more  commonly,  it  is  the  chief 
constituent  of  certain  calculi. 

Of  the  other  abnormal  constituents  of  the  urine  mentioned  it  will  be 
unnecessary  to  speak  at  length  in  this  work. 

Gases. — A  small  quantity  of  gas  is  naturally  present  in  the  urine  in 
a  state  of  solution.  It  consists  of  carbonic  acid  (chiefly)  and  nitrogen 
and  a  small  quantity  of  oxygen. 


THE  METHOD  OF  THE  EXCKETION  OF  UKINE. 

The  excretion  of  the  urine  by  the  kidney  is  believed  to  consist  of  two 
more  or  less  distinct  processes — viz.,  (1.)  of  filtration,  by  which  the  water 
and  the  ready-formed  salts  are  eliminated;  and  (2.)  of  true  secretion,  by 
which  certain  substances  forming  the  chief  and  more  important  part  of 
the  urinary  solids  are  removed  from  the  blood.  This  division  of  function 
corresponds  more  or  less  to  the  division  in  the  functions  of  other  glands 
of  which  we  have  already  treated.  It  will  be  as  well  to  consider  them 
separately. 

(1.)  Of  Filtration. — This  part  of  the  renal  function  is  performed 
within  the  Malpighian  corpuscles  by  the  renal  glomeruli.  By  it  not  only 
the  water  is  strained  off,  but  also  certain  other  constituents  of  the 
urine,  e.g.,  sodium  chloride,  are  separated.  The  amount  of  the  fluid 
filtered  off  depends  almost  entirely  upon  the  blood -pressure  in  the 
glomeruli. 


366  HAND-BOOK    OF    PHYSIOLOGY. 

The  greater  the  blood-pressure  in  the  arterial  system  generally,  and 
consequently  in  the  renal  arteries,  the  greater,  cceteris  paribus,  will  be 
the  blood-pressure  in  the  glomeruli,  and  the  greater  the  quantity  of  urine 
separated;  but  even  without  increase  of  the  general  blood-pressure,  if  the 
renal  arteries  be  locally  dilated,  the  pressure  in  the  glomeruli  will  be 
increased  and  with  it  the  secretion  of  urine.  On  the  other  hand,  if  the 
local  blood-pressure  be  diminished,  the  amount  of  fluid  will  be  lessened. 
All  the  numerous  causes,  therefore,  which  increase  the  blood-pressure  (p. 
152)  will,  as  a  rule,  secondarily  increase  the  secretion  of  urine.  Of  these 
the  heart's  action  is  amongst  the  most  important.  When  its  contractions 
are  increased  in  force,  increased  diuresis  is  the  result.  Similarly,  causes 
which  lower  the  blood-pressure,  e.g.,  enfeebled  action  of  the  heart,  great 
loss  of  blood,  etc.,  will  diminish  the  activity  of  the  secretion  of  urine. 

The  close  connection  between  the  blood-pressure  generally  and  the 
nervous  system  has  been  before  considered,  and  it  will  be  clear,  therefore, 
that  the  amount  of  urine  secreted  depends  greatly  upon  the  influence  of 
the  nervous  system.  Thus,  division  of  the  spinal  cord,  by  producing 
general  vascular  dilatation,  causes  a  great  diminution  of  blood-pressure, 
and  so  diminishes  the  amount  of  water  passed;  since  the  local  dilatation 
in  the  renal  arteries  is  not  sufficient  to  counteract  the  general  diminution 
of  pressure.  Stimulation  of  the  cut  cord  produces,  strangely  enough, 
the  same  results — i.e.,  a  diminution  in  the  amount  of  the  urine  passed, 
but  in  a  different  way,  viz.,  by  constricting  the  arteries  generally,  and, 
among  others,  the  renal  arteries;  the  diminution  of  blood-pressure  result- 
ing from  the  local  resistance  in  the  renal  arteries  being  more  potent  to 
diminish  blood-pressure  in  the  glomeruli  than  the  general  increase  of 
blood-pressure  is  to  increase  it.  Section  of  the  renal  nerves  or  of  any 
others  which  produce  local  dilatation  without  greatly  diminishing  the 
general  blood-pressure  will  cause  an  increase  in  the  quantity  of  fluid 


The  fact  that  in  summer  or  in  hot  weather  the  urine  is  diminished 
may  be  attributed  partly  to  the  copious  elimination  of  water  by  the  skin 
in  the  form  of  sweat  which  occurs  in  summer,  as  contrasted  with  the 
greatly  diminished  functional  activity  of  the  skin  in  winter,  but  also  to 
the  dilated  condition  of  the  vessels  of  the  skin  causing  a  decrease  in  the 
general  blood-pressure.  Thus  we  see  that  in  regard  to  the  elimination 
of  water  from  the  system,  the  skin  and  kidneys  perform  similar  functions, 
and  are  capable  to  some  extent  of  acting  vicariously,  one  for  the  other. 
Their  relative  activities  are  inversely  proportional  to  each  other. 

The  intimate  connection  between  the  condition  of  the  kidney  and  the 
blood-pressure  has  been  exceedingly  well  shown  by  the  introduction  of  an 
instrument  called  the  Oncometer,  recently  introduced  by  Roy,  which  is  a 
modification  of  the  plethysmograph  (Fig.  138).  By  means  of  this  appa- 
ratus any  alteration  in  the  volume  of  the  kidney  is  communicated  to  an 


THE    KIDNEYS    AND    URINE.  367 

apparatus  (oncograph)  capable  of  recording  graphically,  with  a  writing 
ICYCT,  such  variations.  It  lias  been  found  that  the  kidney  is  extremely 
sensitive  to  any  alteration  in  the  general  blood-pressure,  every  fall  in  the 
general  blood-pressure  being  accompanied  by  a  decrease  in  the  volume  of 
the  kidney,  and  every  rise,  unless  produced  by  considerable  constriction 
of  the  peripheral  vessels,  including  those  of  the  kidney,  being  accompanied 
by  a  corresponding  increase  of  volume.  Increase  of  volume  is  followed 
by  an  increase  in  the  amount  of  urine  secreted,  and  decrease  of  volume 
by  a  decrease  in  the  secretion.  In  addition,  however,  to  the  response  of 
the  kidney  to  alterations  in  the  general  blood-pressure,  it  has  been  fur- 
ther observed  that  certain  substances,  when  injected  into  the  blood,  will 
also  produce  an  increase  in  volume  of.  the  kidney,  and  consequent  increased 
now  of  urine,  without  affecting  the  general  blood-pressure — such  bodies 
as  sodium  acetate  and  other  diuretics.  These  observations  appear  to  prove 
that  local  dilatation  of  the  renal  vessel^  may  be  produced  by  alterations 
in  the  blood  upon  a  local  nervous  mechanism,  as  the  effect  is  produced 
when  all  of  the  renal  nerves  have  been  divided.  The  alterations  are  not 
only  produced  by  the  addition  of  drugs,  but  also  by  the  introduction  of 
comparatively  small  quantities  of  water  or  saline  solution.  To  this  altera- 
tion of  the  blood  acting  upon  the  renal  vessels  (either  directly  or)  through 
a  local  vaso- motor  mechanism,  and  not  to  any  great  alteration  in  the 
general  blood-pressure,  must  we  attribute  the  effect  of  meals,  etc.,  ob- 
served by  Roberts.  "The  renal  excretion  is  increased  after  meals  and 
diminished  during  fasting  and  sleep.  The  increase  began  within  the  first 
hour  after  breakfast,  and  continued  during  the  succeeding  two  or  three 
hours;  then  a  diminution  set  in,  and  continued  until  an  hour  or  two  after 
dinner.  The  effect  of  dinner  did  not  appear  until  two  or  three  hours  after 
the  meal;  and  it  reached  its  maximum  about  the  fourth  hour.  From  this 
period  the  excretion  steadily  decreased  until  bedtime.  During  sleep  it 
sank  still  lower,  and  reached  its  minimum — being  not  more  than  one- 
third  of  the  quantity  excreted  during  the  hours  of  digestion."  The  in- 
creased amount  of  urine  passed  after  drinking  large  quantities  of  fluid 
probably  depends  upon  the  diluted  condition  of  the  blood  thereby  in- 
duced. 

The  following  table1  will  help  to  explain  the  dependence  of  the  filtra- 
tion function  upon  the  blood-pressure  and  the  nervous  system: — 

Table  of  the  Relation  of  the  Secretion  of  Urine  to  Arterial  Pressure. 

A.  Secretion  of  Urine  may  be  increased— 

a.  By  increasing  the  general  blood-pressure,  by 

1.  Increase  of  force  or  frequency  of  heart-beat. 

2.  Constriction  of  small  arteries  of  areas  other  than  the  kidney. 

1  Modified  from  M.  Foster. 


368  HAND-BOOK    OF    PHYSIOLOGY. 

b.  By  relaxation  of  the  renal  artery  without  compensating  relaxa- 
tion elsewhere,  by 

1.  Division  of  the  renal  nerves  (causing  polyuria). 

2.  "       and  afterward  stimulating  cord 
below  medulla  (causing  greater  polyuria). 

3.  Division  of  the  splanchnic  nerves;  but  polyuria  is  less  than 

in  1  or  2,  as  these  nerves  are  distributed  to  a  wider  area, 
the  dilatation  of  the  renal  artery  is  accompanied  by  dila- 
tation of  other  vessels,  and  therefore  with  a  somewhat 
diminished  general  blood  supply. 

4.  Puncture  of  the  floor  of  fourth  ventricle  or  mechanical  irri- 

tation of  the  superior  cervical  ganglion  of  the  sympathetic, 
possibly  from  dilatation  of  the  renal  arteries. 

B.  Secretion  of  urine  may  be  diminished — 

a.  By  diminishing  the  general  blood-pressure,  by 

1.  Diminishing  the  force  or  frequency  of  the  heart-beats. 

2.  Dilatation  of  capillary  areas  other  than  the  kidney. 

3.  Division  of  spinal  cord  below  medulla,  which  causes  dilata- 

tion of  general  abdominal  area,  and  urine  generally  ceases 
being  secreted. 

b.  By  increasing  the  blood-presstire,  by  stimulation  of  spinal  cord 

below  medulla,  the  constriction  of  the  renal  artery  not  being 
compensated  for  by  the  increase  of  .general  blood-pressure. 

c.  By  constriction  of  the  renal  artery,  by  stimulating  the  renal  or 

splanchnic  nerves,  or  by  stimulating  the  spinal  cord. 

Although  it  is  convenient  to  call  the  processes  which  go  on  in  the  renal 
glomeruli,  filtration,  there  is  reason  to  believe  that  they  are  not  absolutely 
mechanical,  as  the  term  might  seem  to  imply,  since,  when  the  epithelium 
of  the  Malpighian  capsule  has  been,  as  it  were,  put  out  of  order  by  liga- 
ture of  the  renal  artery,  on  removal  of  the  ligature,  the  urine  has  been 
found  temporarily  to  contain  albumen,  indicating  that  a  selective  power 
resides  in  the  healthy  epithelium,  which  allows  a  certain  constituent  part 
of  the  blood  to  be  filtered  off  and  not  others. 

(2.)  Of  True  Secretion. — That  there  is  a  second  part  in  the  process 
of  the  excretion  of  urine,  which  is  true  secretion,  is  suggested  by  the 
structure  of  the  tubuli  uriniferi,  and  the  idea  is  supported  by  various 
experiments.  It  will  be  remembered  that  the  convoluted  portions  of  the 
tubules  are  lined  with  epithelium,  which  bears  a  close  resemblance  to  the 
secretory  epithelium  of  other  glands,  whereas  the  Malpighian  capsules 
and  portions  of  the  loops  of  Henle  are  lined  simply  by  endothelium.  The 
two  functions  are,  then,  suggested  by  the  differences  of  epithelium,  and 
also  by  the  fact  that  the  blood  supply  is  different,  since  the  convoluted 
tubes  are  surrounded  by  capillary  vessels  derived  from  the  breaking  up  of 
the  efferent  vessels  of  the  Malpighian  tufts.  The  theory  first  suggested 
by  Bowman  (1842),  and  still  generally  accepted,  of  the  function  of  the 


THE    KIDNEYS    AND    URINE.  369 

two  parts  of  the  tubules,,  is  that  the  cells  of  the  convoluted  tubes,  by  a 
process  of  true  secretion,  separate  from  the  blood  substances  such  as 
urea,  whereas  from  the  glomeruli  are  separated  the  water  and  the  inor- 
ganic salts..  Another  theory  suggested  by  Ludwig  (1844)  is  that  in  the 
glomeruli  is  filtered  off  from  the  blood  all  the  constituents  of  the  urine  in 
a  very  diluted  condition.  When  this  passes  along  the  tortuous  uriniferous 
tube,  part  of  the  water  is  re-absorbed  into  the  vessels  surrounding  them, 
leaving  the  urine  in  a  more  concentrated  condition — retaining  all  its 
proper  constituents.  This  osmosis  is  promoted  by  the  high  specific  gravity 
of  the  blood  in  the  capillaries  surrounding  the  convoluted  tubes,  but  the 
return  of  the  urea  and  similar  substances  is  prevented  by  the  secretory 
epithelium  of  the  tubules.  Ludwig's  theory,  however  plausible,  must, 
we  think,  give  way  to  the  first  theory,  which  is  more  strongly  supported 
by  direct  experiment. 

By  using  the  kidney  of  the  newt,  which  has  two  distinct  vascular  sup- 
plies, one  from  the  renal  artery  to  the  glomeruli,  and  the  other  from  the 
renal  portal  vein  to  the  convoluted  tubes,  Nussbaum  has  shown  that  cer- 
tain substances,  e.g.,  peptones,  sugar,  when  injected  into  the  blood,  are 
eliminated  by  the  glomeruli,  and  so  are  not  got  rid  of  when  the  renal 
arteries  are  tied;  whereas  certain  other  substances,  e.g.,  urea,  when  injected 
into  the  blood,  are  eliminated  by  the  convoluted  tubes,  even  when  the 
renal  arteries  have  been  tied.  This  evidence  is  very  direct  that  urea  is 
excreted  by  the  convoluted  tubes. 

Heidenhain  also  has  shown  by  experiment  that  if  a  substance  (sodium 
sulphindigotate),  which  ordinarily  produces  blue  urine,  be  injected  into 
the  blood  after  section  of  the  medulla  which  causes  lowering  of  the  blood- 
pressure  in  the  renal  glomeruli,  that  when  the  kidney  is  examined,  the 
cells  of  the  convoluted  tubules  (and  of  these  alone)  are  stained  with  the 
substance,  which  is  also  found  in  the  lumen  of  the  tubules.  This  appears 
to  show  that  under  ordinary  circumstances  the  pigment  at  any  rate  is 
eliminated  by  the  cells  of  the  convoluted  tubules,  and  that  when  by 
diminishing  the  blood-pressure,  the  filtration  of  urine  ceases,  the  pigment 
remains  in  the  convoluted  tubes,  and  is  not,  as  it  is  under  ordinary  cir- 
cumstances, swept  away  from  them  by  the  flushing  of  them  which  ordi- 
narily takes  place  with  the  watery  part  of  urine  derived  from  the  glom- 
eruli. It  therefore  is  probable  that  the  cells,  if  they  excrete  the  pigment, 
excrete  urea  and  other  substances  also.  But  urea  acts  somewhat  differ- 
ently to  the  pigment,  as  when  it  is  injected  into  the  blood  of  an  animal  in 
which  the  medulla  has  been  divided  and  the  secretion  of  urine  stopped,  a 
copious  secretion  of  urine  results,  which  is  not  the  case  when  the  pigment 
is  used  instead  under  similar  conditions.  The  flow  of  urine,  independent 
of  the  general  blood-pressure,  might  be  supposed  to  be  due  to  the  action 
of  the  altered  blood  upon  some  local  vaso-motor  mechanism;  and,  indeed, 
the  local  blood-pressure  is  directly  affected  in  this  way,  but  there  is  reason 
VOL.  I.— 24. 


370  HAND-BOOK    OF    PHYSIOLOGY. 

for  believing  that  part  of  the  increase  of  the  secretion  is  due  to  the  direct 
stimulation  of  the  cells  by  the  urea  contained  in  the  blood. 

To  sum  up,  then,  the  relation  of  the  two  functions:  (1.)  The  process 
of  nitration,  by  which  the  chief  part  if  not  the  whole  of  t\\Q  fluid  is  elim- 
inated, together  with  certain  inorganic  salts,  and  possibly  other  solids,  is 
directly  dependent  upon  blood-pressure,  is  accomplished  by  the  renal 
glomeruli,  and  is  accompanied  by  a  free  discharge  of  solids  from  the 
tubules.  (2.)  The  process  of  secretion  proper,  by  which  urea  and  the 
principal  urinary  solids  are  eliminated,  is  only  indirectly,  if  at  all,  de- 
pendent upon  blood-pressure,  and  is  accomplished  by  the  cells  of  the  con- 
voluted tubes.  It  is  sometimes  accompanied  by  the  elimination  of  copious 
fluid,  produced  by  the  chemical  stimulation  of  the  epithelium  of  the  same 
tubules. 

SOURCES  OF  THE  NITROGENOUS  URINARY  SOLIDS. 

Urea. — In  speaking  of  the  method  of  the  secretion  of  urine,  it  was 
assumed  that  the  part  played  by  the  cells  of  the  uriniferous  tubules  was 
that  of  mere  separation  of  the  constituents  of  the  urine  which  existed 
ready-formed  in  the  blood:  there  is  considerable  evidence  to  favor  this 
assumption.  What  may  be  called  the  specially  characteristic  solid  of  the 
urine,  i.e.,  urea  (as  well  as  most  of  the  other  solids),  may  be  detected  in 
the  blood,  and  in  other  parts  of  the  body,  e.g.,  the  humors  of  the  eye  (Mil- 
Ion),  even  while  the  functions  of  the  kidneys  are  unimpaired;  but  when 
from  any  cause,  especially  extensive  disease  or  extirpation  of  the  kidneys, 
the  separation  of  urine  is  imperfect,  the  urea  is  found  largely  in  the  blood 
and  in  most  other  fluids  of  the  body. 

It  must,  therefore,  be  clear  that  the  urea  is  for  the  most  part  made 
somewhere  else  than  in  the  kidneys,  and  simply  brought  to  them  by  the 
blood  for  elimination.  It  is  not  absolutely  proved,  however,  that  all  the 
urea  is  formed  away  from  these  organs,  and  it  is  possible  that  a  small 
quantity  is  actually  secreted  by  the  cells  of  the  tubules.  The  sources  of 
the  urea,  which  is  brought  to  the  kidneys  for  excretion,  are  stated  to  be 
two. 

(1.)  From  the  splitting  up  of  the  Elements  ef  the  Nitrogenous  Food. — 
The  origin  of  urea  from  this  source  is  shown  by  the  increase  which  ensues 
on  substituting  an  animal  or  highly  nitrogenous  for  a  vegetable  diet;  in 
the  much  larger  amount — nearly  double — excreted  by  Carnivora  than 
Herbivora,  independent  of  exercise;  and  in  its  diminution  to  about  one- 
half  during  starvation,  or  during  the  exclusion  of  non-nitrogenous  prin- 
ciples of  food.  Part,  at  any  rate,  of  the  increased  amount  of  urea  which 
appears  in  the  urine  soon  after  a  full  meal  of  proteid  material  may  be 
attributed  to  the  production  of  a  considerable  amount  of  leucin  and  ty- 
rosin  as  by-products  of  pancreatic  digestion.  These  substances  are  car- 


THE    KIDNEYS    AND    URINE.  371 

ried  by  the  portal  vein  to  the  liver,  and  it  is  there  that  the  change  in  all 
probability  takes  place;  as  when  the  functions  of  the  organ  are  irrnvolv 
interfered  with,  as  in  the  case  of  acute  yellow  atrophy,  the  amount  of  uiva 
is  distinctly  diminished,  and  its  place  appears  to  be  taken  by  leucin  and 
tyrosin.  It  has  been  found  by  experiment,  too,  that  if  these  substances 
be  introduced  into  the  alimentary  canal,  the  introduction  is  followed  by 
a  corresponding  increase  in  the  amount  of  urea,  but  not  by  the  presence 
of  the  bodies  themselves  in  the  urine. 

(2.) From  the  Nitrogenous  metabolism  of  the  Tissues. — This  second  ori- 
gin of  urea  is  shown  by  the  fact  that  it  continues  to  be  excreted,  though  in 
smaller  quantity  than  usual,  when  all  nitrogenous  substances  are  strictly 
excluded  from  the  food,  as  when  the  diet  consists  for  several  days  of 
sugar,  starch,  gum,  oil,  and  similar  non-nitrogenous  substances  (Lehmann). 
It  is  excreted  also,  even  though  no  food  at  all  be  taken  for  a  considerable 
time;  thus  it  is  found  in  the  urine  of  reptiles  which  have  fasted  for 
months;  and  in  the  urine  of  a  madman  who  had  fasted  eighteen  days, 
Lassaigne  found  both  urea  and  all  the  components  of  healthy  urine. 

Turning  to  the  muscles,  however,  as  the  most  actively  metabolic 
tissue,  we  find  as  a  result  of  their  activity  not  urea,  but  kreatin;  and 
although  it  may  be  supposed  that  some  of  this  latter  body  appears  natur- 
ally as  kreatinin,  yet  it  is  not  in  sufficient  quantity  to  represent  the  large 
amount  of  it  formed  by  the  muscles,  and,  indeed,  by  others  of  the  tissues. 
It  is  assumed  that  kreatin  therefore  is  the  nitrogenous  antecedent  of  urea; 
where  its  conversion  into  urea  takes  place  is  doubtful,  but  very  likely  the 
liver,  and  possibly  the  spleen,  may  be  the  seats  of  the  change.  It  may  be, 
however,  that  part — but  if  so,  a  small  part — reaches  the  kidneys  without 
previous  change,  leaving  it  to  the  cells  of  the  renal  tubules  to  complete  the 
action.  In  speaking  of  kreatin  as  the  antecedent  of  urea,  it  should  be 
recollected  that  other  nitrogenous  products,  such  as  xanthin  (C6H4N402), 
appear  in  conjunction  with  it,  and  that  these  may  also  be  converted  into 
urea. 

It  was  formerly  taken  for  granted  that  the  quantity  of  urea  in  the 
urine  is  greatly  increased  by  active  exercise;  but  numerous  observers  have 
failed  to  detect  more  than  a  slight  increase  under  such  circumstances;  and 
our  notions  concerning  the  relation  of  this  excretory  product  to  the  de- 
struction of  muscular  fibre,  consequent  on  the  exercise  of  the  latter,  have 
undergone  considerable  modification.  There  is  no  doubt,  of  course,  that 
like  all  parts  of  the  body,  the  muscles  have  but  a  limited  term  of  exist- 
ence, and  are  being  constantly  although  very  slowly  renewed,  at  the  same 
time  that  a  part  of  the  products  of  their  disintegration  appears  in  the 
urine  in  the  form  of  urea.  But  the  waste  is  not  so  fast  as  it  was  formerly 
supposed  to  be;  and  the  theory  that  the  amount  of  work  done  by  the 
muscle  is  expressed  by  the  quantity  of  urea  excreted  in  the  urine  must 
without  doubt  be  given  up. 


372  HAND-BOOK    OF    PHYSIOLOGY. 

Uric  Acid. — Uric  acid  probably  arises  much  in  the  same  way  as  urea, 
either  from  the  disintegration  of  albuminous  tissues,  or  from  the  food. 
The  relation  which  uric  acid  and  urea  bear  to  each  other  is,  however,  still 
obscure:  but  uric  acid  is  said  to  be  a  less  advanced  stage  of  the  oxidation 
of  the  products  of  proteid  metabolism.  The  fact  that  they  often  exist 
together  in  the  same  urine,  makes  it  seem  probable  that  they  have  differ- 
ent origins;  but  the  entire  replacement  of  either  by  the  other,  as  of  urea 
by  uric  acid  in  the  urine  of  birds,  serpents,  and  many  insects,  and  of  uric 
acid  by  urea,  in  the  urine  of  the  feline  tribe  of  Mammalia,  shows  that 
either  alone  may  take  the  place  of  the  two.  At  any  rate,  although  it  is 
true  that  one  molecule  of  uric  acid  is  capable  of  splitting  up  into  two 
molecules  of  urea  and  one  of  mes-oxalic  acid,  there  is  no  evidence  for 
believing  that  uric  acid  is  an  antecedent  of  urea  in  the  nitrogenous 
metabolism  of  the  body.  Some  experiments  seem  to  show  that  uric  acid 
is  formed  in  the  kidney. 

Hippuric  Acid  (C9H9N03). — Hippuric  acid  is  closely  allied  to  benzoic 
acid;  and  this  substance  when  introduced  into  the  system,  is  excreted  by 
the  kidneys  as  hippuric  acid  (lire).  Its  source  is  not  satisfactorily  deter- 
mined: in  part  it  is  probably  derived  from  some  constituents  of  vegetable 
diet,  though  man  has  no  hippuric  acid  in  his  food,  nor, 'commonly,  any 
benzoic  acid  that  might  be  converted  into  it;  in  part  from  the  natural 
disintegration  of  tissues,  independent  of  vegetable  food,  for  Weismann 
constantly  found  an  appreciable  quantity,  even  when  li<  ng  on  an  exclu- 
sively animal  diet.  Hippuric  acid  arises  from  the  union  of  benzoic  acid 
with  glycin  (C2H5N02  +  C7H6O2  =  C9H9N03  +  H20),  which  union  may 
take  place  in  the  kidneys  themselves,  as  well  as  in  the  liver. 

Extractives. — The  source  of  the  extractives  of  the  urine  is  probably 
in  chief  part  the  disintegration  of  the  nitrogenous  tissues,  but  we  are 
unable  to  say  whether  these  nitrogenous  bodies  are  merely  accidental, 
having  resisted  further  decomposition  into  urea,  or  whether  they  are  the 
representatives  of  the  decomposition  of  special  tissues,  or  of  special  forms 
of  metabolism  of  the  tissues.  There  is*  however,  one  exception,  and  this 
is  in  the  case  of  kreatinin;  there  is  great  reason  for  believing  that  the 
amount  of  this  body  which  appears  in  the  urine  is  derived  from  the  metab- 
olism of  the  nitrogenous  food,  as  when  this  is  diminished,  it  diminishes, 
and  when  stopped,  it  no  longer  appears  in  the  urine. 

THE  PASSAGE  OF  URINE  INTO  THE  BLADDER. 

As  each  portion  of  urine  is  secreted  it  propels  that  which  is  already 
in  the  tubes  onward  into  the  pelvis  of  the  kidney.  Thence  through  the 
ureter  the  urine  passes  into  the  bladder,  into  which  its  rate  and  mode  of 
entrance  has  been  watched  in  cases  of  ectopia  vesicce,  i.e.,  of  such  fissures 
in  the  anterior  or  lower  part  gf  the  walls  of  the  abdomen,  and  of  the  front 


THE    KIDNEYS    AND    URINE.  373 

wall  of  the  bladder,  as  expose  to  view  its  hinder  wall  together  with  the 
orifices  of  the  ureters.  The  urine  does  not  enter  the  bladder  at  any  reg- 
ular rate,  nor  is  there  a  synchronism  in  its  movement  through  the  two 
ureters.  During  fasting,  two  or  three  drops  enter  the  bladder  every 
minute,  each  drop  as  it  enters  first  raising  up  the  little  papilla  on  which, 
in  these  cases,  the  ureter  opens,  and  then  passing  slowly  through  its  orifice, 
which  at  once  again  closes  like  a  sphincter.  In  the  recumbent  posture, 
the  urine  collects  for  a  little  time  in  the  ureters,  then  flows  gently,  and, 
if  the  body  be  raised,  runs  from  them  in  a  stream  till  they  are  empty. 
Its  flow  is  increased  in  deep  inspiration,  or  straining,  and  in  active  exer- 
cise, and  in  fifteen  or  twenty  minutes  after  a  meal  (Erichsen).  The 
urine  collecting  is  prevented  from  regurgitation  into  the  ureters  by  the 
mode  in  which  these  pass  through  the  walls  of  the  bladder,  namely,  by 
their  lying  for  between  half  and  three-quarters  of  an  inch  between  the 
muscular  and  mucous  coats  before  they  turn  rather  abruptly  forward, 
and  open  through  the  latter  into  the  interior  of  the  bladder. 

Micturition. — The  contraction  of  the  muscular  walls  of  the  bladder 
may  by  itself  expel  the  urine  with  little  or  no  help  from  other  muscles, 
when  the  sphincter  of  the  organ  is  relaxed.  In  so  far,  however,  as  it  is  a 
voluntary  act,  micturition  is  performed  by  means  of  the  abdominal  and 
other  expiratory  muscles  which,  in  their  contraction,  press  on  the  abdom- 
inal viscera,  the  diaphragm  being  fixed,  and  cause  the  expulsion,  of  the 
contents  of  the  bladder.  The  muscular  coat  of  the  bladder  co-operates, 
in  micturition,  by  reflex  involuntary  action,  with  the  abdominal  muscles; 
and  the  act  is  completed  by  the  accelerator  urince,  which,  as  its  name 
implies,  quickens  the  stream,  and  expels  the  last  drops  of  urine  from  the 
urethra.  The  act,  so  far  as  it  is  not  directed  by  volition,  is  under  the 
control  of  a  nervous  centre  in  the  lumbar  spinal  cord,  through  which,  as 
in  the  case  of  the  .similar  centre  for  defaecation  (p.  288),  the  various 
muscles  concerned  are  harmonized  in  their  action.  It  is  well  known  that 
the  act  may  be  reflexly  induced,  e.g.,  in  children  who  suffer  from  intes- 
tinal worms,  or  other  such  irritation.  Generally  the  afferent  impulse 
which  calls  into  action  the  desire  to  micturate  is  excited  by  over  disten- 
tion  of  the  bladder,  or  even  by  a  few  drops  of  urine  passing  into  the 
urethra. 


END   OF   VOL.    I. 


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